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NCERT Exemplar Class 10 Science Chapter 5 Periodic Classifications of Elements Solutions

NCERT Exemplar Solutions for Class 10 Science Chapter 5 Periodic Classifications of Elements covers all the important questions and answers as well as advanced level questions. It helps in learning about the periodic table, Dobereiner’s Triads, Newland's Law of Octaves, Mendeleev’s Periodic Table, Modern Periodic Table and Groups in Modern Periodic Table.

The NCERT Exemplar solutions for class 10 science is very important for board exams. NCERT Exemplar Solutions for Class 10 Science Chapter 5 Periodic Classifications of Elements is provided by our experts. They prepared the best solutions which help the students in understanding the solutions in an easy way. This chapters also covers the other topics like akali metals, alkaline metals, chalcogens, halogens and noble gases.


Chapter Name

Chapter 5 Periodic Classifications of Elements

Book Title

NCERT Exemplar for Class 10 Science

Related Study

  • NCERT Solutions for Class 10 Science Chapter 5 Periodic Classifications of Elements
  • Revision Notes for Class 10 Science Chapter 5 Periodic Classifications of Elements
  • MCQ for Class 10 Science Chapter 5 Periodic Classifications of Elements
  • Important Questions for Class 10 Science Chapter 5 Periodic Classifications of Elements

Topics Covered

  • MCQ
  • Short Answers Questions
  • Long Answers Questions

NCERT Exemplar Solutions for Chapter 5 Periodic Classifications of Elements Class 10 Science

Multiple Choice Questions

1. Upto which element, the Law of Octaves was found to be applicable
(a) Oxygen
(b) Calcium
(c) Cobalt
(d) Potassium

Solution

(b) Calcium 

Newland’s law of octaves was applicable to the elements with atomic mass up to 40 da which comes up to Calcium. After calcium every eighth element possess properties similar to that of the first.


2. According to Mendeleev's ′ Periodic Law, the elements were arranged in the periodic table in the order of
(a) increasing atomic number
(b) decreasing atomic number
(c) increasing atomic masses
(d) decreasing atomic masses

Solution

(c) increasing atomic masses


3. In Mendeleev ’s Periodic Table, gaps were left for the elements to be discovered later. Which of the following elements found a place in the perioidc table later
(a) Germanium
(b) Chlorine
(c) Oxygen
(d) Silicon

Solution

(a) Germanium 

Mendeleev name unnamed elements as EKA- Boron EKA- Aluminium and EKA Silicon which were later replaced as Scandium, Gallium, and germanium respectively.


4. Which of the following statement (s) about the Modern Periodic Table are incorrect
(i) The elements in the Modern Periodic Table are arranged on the basis of their decreasing atomic number
(ii) The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic masses
(iii) Isotopes are placed in adjoining group (s) in the Periodic Table
(iv) The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic number

(a) (i) only
(b) (i), (ii) and (iii)
(c) (i), (ii) and (iv)
(d) (iv) only

Solution

(b) (i) (ii) and (iii) 

Elements in the Modern Periodic Table are arranged on the basis of their increasing atomic number. Atomic mass is not a criterion for classification in the modern periodic table atomic mass is not a criteria. Isotopes are given the same position in periodic table.

5. Which of the following statements about the Modern Periodic Table is correct:
(a) It has 18 horizontal rows known as Periods
(b) It has 7 vertical columns known as Periods
(c) It has 18 vertical columns known as Groups
(d) It has 7 horizontal rows known as Groups

Solution

(c) It has 18 vertical columns known as Groups

Modern periodic table has18 groups and 7 periods. Columns are called groups and rows are called periods


6.  Which of the given elements A, B, C, D and E with atomic number 2, 3, 7, 10 and 30 respectively belong to the same period?
(a) A, B, C
(b) B, C, D
(c) A, D, E
(d) B, D, E

Solution

(b) B, C, D 

Element with atomic number2belong to first period and element with atomic number from 3 to 10 belong to second period.


7. The elements A, B, C, D and E have atomic number 9, 11, 17, 12 and 13 respectively. Which pair of elements belong to the same group?
(a) A and B
(b) B and D
(c) A and C
(d) D and E

Solution

(c) A and C 

A and C are fluorine and chlorine respectively and they belong to the same group.


8. Where would you locate the element with electronic configuration 2,8 in the Modern Periodic Table? (a) Group 8
(b) Group 2
(c) Group 18
(d) Group 10

Solution

(c) Group 18 

Element in group 18 have their outermost shells completely filled..


9. An element which is an essential constituent of all organic compounds belongs to
(a) group 1
(b) group 14
(c) group 15
(d) group 16

Solution

(b) group 14 

All organic compounds contain carbon, which belongs to group 14.


10. Which of the following is the outermost shell for elements of period 2?
(a) K shell
(b) L shell
(c) M shell
(d) N shell

Solution

(b) L shell 

There are two shells K and L in period 18.


11. Which one of the following elements exhibit maximum number of valence eletrons ? 
(a) Na 
(b) Al 
(c) Si 
(d) P 

Solution

(d) P 

Electronic configuration of Na, Al, Si and P are 2,8 1, 2,8,3,2,8,4, and 2,8,5 respectively. Valence electrons in Na, Al, Si and P are 1,3,4 and 5.Therefore,Phas maximum number of valence electrons.


12. Which of the following gives the correct increasing order of the atomic radii of O, F and N ?
(a) O, F, N
(b) N, F, O
(c) O, N, F
(d) F, O, N

Solution

(d) F, O, N 

As one moves from left to right across a period, the atomic radius increases. N(7), O(8) and F(10) are in increasing order of atomic numbers.


13. Which among the following elements has the largest atomic radii ? 
(a) Na 
(b) Mg 
(c) K 
(d) Ca 

Solution

(c)  K 

K has largest atomic radii. The atomic radius decreases as one moves from left to right along a period. This happens because the nuclear charge increases, which tends to pull the electron closer to the nucleus thereby reducing the size of the atom.


14. Which of the following elements would lose an electron easily ? 
(a) Mg
(b) Na 
(c) K 
(d) Ca 

Solution

(b) Na 

Na and K belongs to the group I and Mg and Ca belong to group II. Na has 1 electron in its valence shell which can be lost easily.


15. Which of the following elements does not lose an electron easily ? 
(a) Na 
(b) F 
(c) Mg 
(d) Al 

Solution

(d) Al

Sodium, magnesium and aluminium have1, 2 and 3 electrons respectively in its outermost shell whereas fluorine has 7 electrons in its outermost shell. Therefore, fluorine does not lose electron easily.

 

16. Which of the following are the characteristics of isotopes of an element?
(i) Isotopes of an element have same atomic masses
(ii) Isotopes of an element have same atomic number
(iii) Isotopes of an element show same physical properties
(iv) Isotopes of an element show same chemical properties

(a) (i), (iii) and (iv)
(b) (ii), (iii) and (iv)
(c) (ii) and (iii)
(d) (ii) and (iv)

Solution

(d) (ii) and (iv) 

Elements with same atomic number but different atomic masses are known as isotopes. Isotopes have same chemical properties but different physical properties.


17. Arrange the following elements in the order of their decreasing metallic character Na, Si, Cl, Mg, Al
(a) Cl > Si >Al > Mg >Na
(b) Na >Mg >Al >Si > Cl
(c) Na > Al > Mg > Cl > Si
(d) Al > Na> Si > Ca> Mg

Solution

(b) Na >Mg >Al >Si > Cl

Sodium, magnesium, aluminium and chlorine have 1, 2, 3 and 7electrons in their valence shells respectively. Hence, sodium shows maximum metallic characters followed by magnessium, aluminium and chlorine shows non-metallic properties.


18. Arrange the following elements in the order of their increasing nonmetallic character Li, O, C, Be, F
(a) F < O < C < Be < Li
(b) Li < Be < C < O< F
(c) F < O < C < Be < Li
(d) F < O < Be < C < Li

Solution

(b) Li < Be < C < O< F

Li is on the left of in the 2nd period of modern periodic table followed by berrylium. Fluorine is at right next to Neon. Hence Fluorine shows maximum non-metallic characters followed by Oxygen, Berrylium, carbon and Lithium.


19.  What type of oxide would Eka– aluminium form?

(a) EO3
(b) E3O2
(c) E2O3
(d) EO

Solution

(c) E2 O3


20. Three elements B, Si and Ge are
(a) metals
(b) non-metals
(c) metalloids
(d) metal, non-metal and metalloid respectively

Solution

(c) metalloids


21. Which of the following elements will form an acidic oxide?
(a) An element with atomic number 7
(b) An element with atomic number 3
(c) An element with atomic number 12
(d) An element with atomic number 19

Solution

(a) An element with atomic number 7

The electronic configuration of an element with atomic number 7 is2,5. This means that the element can gain 3 electrons and thereby is an electronegative element. Therefore, it should be a non-metal and non-metals form acidic oxides.


22. The element with atomic number 14 is hard and forms acidic oxide and a covalent halide. To which of the following categories does the element belong?
(a) Metal
(b) Metalloid
(c) Non-metal
(d) Left-hand side element

Solution

(b) Metalloid 

Element with atomic no. 14 is Silicon and it is a metalloid. Silicon forms acidic oxide, there by behaving as a non-metal. It also forms covalent halides, thus acting as a metal as well.


23.  Which one of the following depict the correct representation of atomic radius(r) of an atom?

(a) (i) and (ii) 
(b) (ii) and (iii) 
(c) (iii) and (iv) 
(d) (i) and (iv) 

Solution

(b) (ii) and (iii) 

The distance between the nucleus and outermost orbital is known as the atomic radius. The atomic radius is shown clearly in images (ii) and (iii).


24. Which one of the following does not increase while moving down the group of the periodic table? (a) Atomic radius
(b) Metallic character
(c) Valence
(d) Number of shells in an element
Solution
(c) Valence
Valency remains thesame in a group.

25. On moving from left to right in a period in the periodic table, the size of the atom.
(a) increases
(b) decreases
(c) does not change appreciably
(d) first decreases and then increases
Solution
(b) decreases 

When one moves from left to right in a period then the atomic radius also decreases. Therefore, the size of the atom also decreases.


26. Which of the following set of elements is written in order of their increasing metallic character?
(a) Be Mg Ca
(b) Na Li K
(c) Mg Al Si
(d) C O N

Solution

(a) Be  Mg  Ca

As we move down the group, the metallic character increases. In the elements that belong to same group Be is at the top and Ca is at the bottom.


Short Answer Questions 

27. The three elements A, B and C with similar properties have atomic masses X, Y and Z respectively. The mass of Y is approximately equal to the average mass of X and Z. What is such an arrangement of elements called as? Give one example of such a set of elements.

Solution

The arrangement of these elements is known as Dobereiner’s triad. One example of such arrangement is, Lithium, Sodium and Potassium.


28. Elements have been arranged in the following sequence on the basis of their increasing atomic masses. F, Na, Mg, Al, Si, P, S, Cl, Ar, K (a) Pick two sets of elements which have similar properties. (b) The given sequence represents which law of classification of elements?

Solution

(a) The following set of elements have similar properties:

  1. F and Cl
  2. Na and K

(b) The given sequence represents Newland’s law of octaves.


29. Can the following groups of elements be classified as Dobereiner's triad ?
(a) Na, Si, Cl
(b) Be, Mg, Ca
Atomic mass of Be 9; Na 23; Mg 24; Si 28; Cl 35; Ca 40

Explain by giving reason. 

Solution

(a) The atomic mass of Silicon is the average of atomic masses of Sodium and Chlorine. But these elementsdo not have similar properties. This is the reason why they cannot be classified as Dobereiner’s triad.

(b) Yes, Be, Mg and Ca can be classified as Dobereiner’s triad because they have similar properties. Also the mass of magnesium (Mg) is roughly the average of the atomic mass of Be and Ca..


30. In Mendeleev’s Periodic Table the elements were arranged in the increasing order of their atomic masses. However, cobalt with atomic mass of 58.93 amu was placed before nickel having an atomic mass of 58.71 amu. Give reason for the same.

Solution

There are instances where elements with higher atomic mass are placed before the element with lower atomic mass in Mendeleev’s Period Table. This was done to ensure that elements with similar properties were included in the same group. As a result cobalt was placed before nickel despite of greater atomic number.


31. “Hydrogen occupies a unique position in Modern Periodic Table”. Justify the statement. 

Solution

Hydrogen occupies a unique position in Modern Periodic Table because of the following reasons.

  • Hydrogen has an outer electronic configuration similar to that of alkali metals. Hydrogen and alkali metals have one electron in their outermost shell.
  • Properties of hydrogen are also similar to that of halogens as electronic configurations of halogens and hydrogen are same.


32. Write the formulae of chlorides of Eka-silicon and Eka-aluminium, the elements predicted by Mendeleev. 

Solution

Chlorides of Eka - silicon: ECl4 
Chlorides of Eka - Aluminium : ECl3  


33. Three elements A, B and C have 3, 4 and 2 electrons respectively in their outermost shell. Give the group number to which they belong in the Modern Periodic Table. Also, give their valencies. 

Solution

  • A belongs to Group 13, B belongs to Group 14 and C belongs to Group 2.
  • Valency of A is 3, B is 4 and C is 2.


34. If an element X is placed in group 14, what will be the formula and the nature of bonding of its chloride ? 

Solution

As element X is placed in group 14,it has 4 electrons in its outermost orbit. The formula of its chloride will be ECl4.Theelement can form compound by sharing the valence electrons hence chemical bonding takes place.


35. Compare the radii of two species X and Y. Give reasons for your answer.
(a) X has 12 protons and 12 electrons
(b) Y has 12 protons and 10 electrons

Solution

From electron arrangement 

X - 2.8.2
Y - 2.8 
The atomic radius of Y will be smaller than that of Y as it has fewer energy levels.


36. Arrange the following elements in increasing order of their atomic radii.
(a) Li, Be, F, N
(b) Cl, At, Br I

Solution

Given elements are in the same group and are arranged from left to right. So, increasing order of their atomic radii
(a) Li>Be>F>N
(b) Cl>Br>I>At


37.  Identify and name the metals out of the following elements whose electronic configurations are given below.
(a) 2, 8, 2
(b) 2, 8, 1
(c) 2, 8, 7
(d) 2, 1

Solution

(a) Magnesium
(b) Sodium
(c) Chlorine
(d) Lithium


38. Write the formula of the product formed when the element A (atomic number 19) combines with the element B (atomic number 17). Draw its electronic dot structure. What is the nature of the bond formed?

Solution

Element A is K (Potassium). The electronic configuration of element A (atomic number 19) would be 2, 8, 8, 1.

Element B is Cl (Chlorine).The electronic configuration of element B (atomic number 17) would be 2, 8, 7. 

An ionic bond is usually formed when a metal and a non-metal combine. Metals have tendency to lose electrons to form cations whereas non-metals accept the electrons to form anions.

Dot structure:

Potassium and chlorine will combine to form potassium chloride (KCl).

The electron dot structure of KCl is as given below:


39. Arrange the following elements in the increasing order of their metallic character Mg, Ca, K, Ge, Ga 

Solution

Ge > Ga > Mg > Ca > K


40. Identify the elements with the following property and arrange them in increasing order of their reactivity
(a) An element which is a soft and reactive metal
(b) The metal which is an important constituent of limestone
(c) The metal which exists in liquid state at room temperature

Solution

(a) Na or K

(b) Ca 

(c) Hg The increasing order of reactivity of the elements is:
Hg < Ca < Na < K


41. Properties of the elements are given below. Where would you locate the following elements in the periodic table?
(a) A soft metal stored under kerosene
(b) An element with variable (more than one) valency stored under water.
(c) An element which is tetravalent and forms the basis of organic chemistry
(d) An element which is an inert gas with atomic number 2
(e) An element whose thin oxide layer is used to make other elements corrosion resistant by the process of “ anodising” . 

Solution

(a) Sodium (Na) Group 1 and Period 3 or Potassium (K) Group 1 and Period 4

(b) Phosphorus (P) Group 15 and Period 3

(c) Carbon (C) Group 14 and Period 2

(d) Helium (He) Group 18 and Period 1

(e) Aluminium (Al) Group 13 and Period 3


Long Answer Questions 

42. An element is placed in 2nd Group and 3rd Period of the Periodic Table, burns in presence of oxygen to form a basic oxide.
(a) Identify the element
(b) Write the electronic configuration
(c) Write the balanced equation when it burns in the presence of air
(d) Write a balanced equation when this oxide is dissolved in water (e) Draw the electron dot structure for the formation of this oxide

Solution

(a)  Element is Magnessium 
(b) Electronic Configuration  - 2, 8, 2
(c) 2Mg + O2 → 2MgO
(d) MgO + H2O → Mg(OH)2


43. An element X (atomic number 17) reacts with an element Y (atomic number 20) to form a divalent halide.
(a) Where in the periodic table are elements X and Y placed?
(b) Classify X and Y as metal (s), non-metal (s) or metalloid (s)
(c) What will be the nature of oxide of element Y? Identify the nature of bonding in the compound formed (d) Draw the electron dot structure of the divalent halide

Solution 

(a) X belongs to Group 17 and 3rd period and Y belongs to Group 2 and 4th period.

(b) X is anon-metal and Y is a metal.

(c) The oxides of element Y will be basic in nature. Ionic bonding is present in the oxide of element Y.
(d)

Electron dot-structure for calcium chloride


44. Atomic number of a few elements are given below 10, 20, 7, 14
(a) Identify the elements
(b) Identify the Group number of these elements in the Periodic Table
(c) Identify the Periods of these elements in the Periodic Table
(d) What would be the electronic configuration for each of these elements?
(e) Determine the valency of these elements

Solution

(a) Elements are Neon (10), Calcium (20), Nitrogen (7), Silicon (14).

(b) The elements belong to the following group:

  • Neon –18
  • Calcium –2
  • Nitrogen –15
  • Silicon -14

(c) The elements belong to the following period:

  • Neon –2
  • Calcium –4
  • Nitrogen –2
  • Silicon -3

(d) The electron configuration of the elements are as follows: 

  • Neon –2, 8
  • Calcium –2, 8, 8, 2
  • Nitrogen –2, 5
  • Silicon –2, 8, 4

(e) The valency of the elements is as follows:

  • Neon –0
  • Calcium –2
  • Nitrogen –3
  • Silicon –4


45. Complete the following cross word puzzle (figure 5.1)

Across : 
(i) An element with atomic number 12. 
(iii) Metal used in making cans and member of group 14.
(iv) A lustrous non - metal which has 7 electrons in its oiutermost shell. 

Down : 
(ii) Highly reactive and soft metal which imparts yellow colour when subjected to flame and is kept in kerosene.
(v) The first element of second Period
(vi) An element which is used in making fluorescent bulbs and is second member of Group 18 in the Modern Periodic Table
(vii) A radioactive element which is the last member of halogen family.
(viii) Metal which is an important constituent of steel and forms rust when exposed to moist air.
(ix) The first metalloid in Modern Periodic Table whose fibres are used in making bullet-proof vests 

Solution

Across
(1) Magnesium
(3) Tin
(4) Iodine
Down
(2) Sodium
(5) Lithium
(6) Neon
(7) Astatine
(8) Iron
(9) Boron

46. (a) In this ladder (Figure 5.2) symbols of elements are jumbled up. Rearrange these symbols of elements in the increasing order of their atomic number in the Periodic Table.
(b) Arrange them in the order of their group also.
Solution
(a) H, He, Li, Be, B, C, N, O, F, Ne, Mg, Al Si,P, S, Cl, Ar, K, Ca
b) Group 1:H, Li, Na, K
Group 2: Be, Mg, Ca
Group 13: B. Al
Group 14: C, Si
Group 15: N. P
Group 16: 0, S
Group 17: F. U
Group 18: He, Ne, Ar

47. Mendeleev ′ predicted the existence of certain elements not known at that time and named two of them as Eka-silicon and Eka-aluminium.
(a) Name the elements which have taken the place of these elements
(b) Mention the group and the period of these elements in the Modern Periodic Table.
(c) Classify these elements as metals, non-metals or metalloids
(d) How many valence electrons are present in each one of them?

Solution

(a) Eka-Silicon was replaced by germanium, Eka-aluminium was replaced by Gallium

(b) Germanium-Group 14 Period 5

Gallium-Group 13 Period 5

(c) Germanium is a metalloid and Gallium is a metal.

(d) Germanium has 4 electron, Gallium has 3 valence electrons.


48. (a) Electropositive nature of the element(s) increases down the group and decreases across the period
(b) Electronegativity of the element decreases down the group and increases across the period
(c) Atomic size increases down the group and decreases across a period (left to right)
(d) Metallic character increases down the group and decreases across a period.
On the basis of the above trends of the Periodic Table, answer the following about the elements with atomic numbers 3 to 9.
(a) Name the most electropositive element among them
(b) Name the most electronegative element
(c) Name the element with smallest atomic size
(d) Name the element which is a metalloid
(e) Name the element which shows maximum valency.
Solution
(a) Lithium is the most electropositive element.
(b) Fluorine is the most electronegative element.
(c) Fluorine has thesmallest atomic size among the given elements.
(d) Boronis a metalloid.
(e) Carbon shows maximum valency.

49. An element X which is a yellow solid at room temperature shows catenation and allotropy. X forms two oxides which are also formed during the thermal decomposition of ferrous sulphate crystals and are the major air pollutants.
(a) Identify the element X
(b) Write the electronic configuration of X
(c) Write the balanced chemical equation for the thermal decomposition of ferrous sulphate crystals?
(d) What would be the nature (acidic/ basic) of oxides formed?
(e) Locate the position of the element in the Modern Periodic Table
Solution
(a) Element X is Sulphur 
(b) 2, 8, 6
(c) 2FeSO4 → Fe2O3 + SO2 + SO3
(d) Sulphur oxides are acidic in nature
(e) Group 16 Period 3

50. An element X of group 15 exists as diatomic molecule and combines with hydrogen at 773 K in presence of the catalyst to form a compound, ammonia which has a characteristic pungent smell. (a) Identify the element X. How many valence electrons does it have?
(b) Draw the electron dot structure of the diatomic molecule of X. What type of bond is formed in it?
(c) Draw the electron dot structure for ammonia and what type of bond is formed in it?
Solution
(a) Answer is Nitrogen and it has 5 electrons in its outermost shell. 
(b)
(c) Ammonia forms covalent bonding

51. Which group of elements could be placed in Mendeleev's ′ Periodic Table without disturbing the original order? Give reason.
Solution
According to Mendeleev’s periodic table, the properties of elements are the periodic function of their atomic masses. There is a periodic recurrence of elements with similar physical and chemical properties. Noble gas being inert could be placed in a separate group without disturbing the original order.

52. Give an account of the process adopted by Mendeleev ′ for the classification of elements. How did he arrive at “Periodic Law”?
Solution
The number of known elements at Mendeleev’s time was 63. He examined the correlation between chemical properties and atomic masses of elements. He studied the compounds which the known elements formed with hydrogen and oxygen. Hydrogen and oxygen were selected by Mendeleev because these elements form compound with most of the other elements. Mendeleev then made 63 cards and wrote the name of an element on each card: along with the chemical properties of a particular element. He then pinned those cards on a wall. He observed that most of the elements can be arranged in periodic table in increasing order of their atomic masses. That is how Mendeleev arrived at “Periodic law”. Mendeleev’s Periodic Law states that properties of elements are periodic function of their atomic masses.

NCERT Exemplar Chapter 5 Periodic Classifications of Elements Class 10 Science Solutions

NCERT Exemplar Class 10 Science Chapter 5 Periodic Classifications of Elements Solutions

NCERT Exemplar Solutions for Class 10 Science Chapter 5 Periodic Classifications of Elements covers all the important questions and answers as well as advanced level questions. It helps in learning about the periodic table, Dobereiner’s Triads, Newland's Law of Octaves, Mendeleev’s Periodic Table, Modern Periodic Table and Groups in Modern Periodic Table.

The NCERT Exemplar solutions for class 10 science is very important for board exams. NCERT Exemplar Solutions for Class 10 Science Chapter 5 Periodic Classifications of Elements is provided by our experts. They prepared the best solutions which help the students in understanding the solutions in an easy way. This chapters also covers the other topics like akali metals, alkaline metals, chalcogens, halogens and noble gases.


Chapter Name

Chapter 5 Periodic Classifications of Elements

Book Title

NCERT Exemplar for Class 10 Science

Related Study

  • NCERT Solutions for Class 10 Science Chapter 5 Periodic Classifications of Elements
  • Revision Notes for Class 10 Science Chapter 5 Periodic Classifications of Elements
  • MCQ for Class 10 Science Chapter 5 Periodic Classifications of Elements
  • Important Questions for Class 10 Science Chapter 5 Periodic Classifications of Elements

Topics Covered

  • MCQ
  • Short Answers Questions
  • Long Answers Questions

NCERT Exemplar Solutions for Chapter 5 Periodic Classifications of Elements Class 10 Science

Multiple Choice Questions

1. Upto which element, the Law of Octaves was found to be applicable
(a) Oxygen
(b) Calcium
(c) Cobalt
(d) Potassium

Solution

(b) Calcium 

Newland’s law of octaves was applicable to the elements with atomic mass up to 40 da which comes up to Calcium. After calcium every eighth element possess properties similar to that of the first.


2. According to Mendeleev's ′ Periodic Law, the elements were arranged in the periodic table in the order of
(a) increasing atomic number
(b) decreasing atomic number
(c) increasing atomic masses
(d) decreasing atomic masses

Solution

(c) increasing atomic masses


3. In Mendeleev ’s Periodic Table, gaps were left for the elements to be discovered later. Which of the following elements found a place in the perioidc table later
(a) Germanium
(b) Chlorine
(c) Oxygen
(d) Silicon

Solution

(a) Germanium 

Mendeleev name unnamed elements as EKA- Boron EKA- Aluminium and EKA Silicon which were later replaced as Scandium, Gallium, and germanium respectively.


4. Which of the following statement (s) about the Modern Periodic Table are incorrect
(i) The elements in the Modern Periodic Table are arranged on the basis of their decreasing atomic number
(ii) The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic masses
(iii) Isotopes are placed in adjoining group (s) in the Periodic Table
(iv) The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic number

(a) (i) only
(b) (i), (ii) and (iii)
(c) (i), (ii) and (iv)
(d) (iv) only

Solution

(b) (i) (ii) and (iii) 

Elements in the Modern Periodic Table are arranged on the basis of their increasing atomic number. Atomic mass is not a criterion for classification in the modern periodic table atomic mass is not a criteria. Isotopes are given the same position in periodic table.

5. Which of the following statements about the Modern Periodic Table is correct:
(a) It has 18 horizontal rows known as Periods
(b) It has 7 vertical columns known as Periods
(c) It has 18 vertical columns known as Groups
(d) It has 7 horizontal rows known as Groups

Solution

(c) It has 18 vertical columns known as Groups

Modern periodic table has18 groups and 7 periods. Columns are called groups and rows are called periods


6.  Which of the given elements A, B, C, D and E with atomic number 2, 3, 7, 10 and 30 respectively belong to the same period?
(a) A, B, C
(b) B, C, D
(c) A, D, E
(d) B, D, E

Solution

(b) B, C, D 

Element with atomic number2belong to first period and element with atomic number from 3 to 10 belong to second period.


7. The elements A, B, C, D and E have atomic number 9, 11, 17, 12 and 13 respectively. Which pair of elements belong to the same group?
(a) A and B
(b) B and D
(c) A and C
(d) D and E

Solution

(c) A and C 

A and C are fluorine and chlorine respectively and they belong to the same group.


8. Where would you locate the element with electronic configuration 2,8 in the Modern Periodic Table? (a) Group 8
(b) Group 2
(c) Group 18
(d) Group 10

Solution

(c) Group 18 

Element in group 18 have their outermost shells completely filled..


9. An element which is an essential constituent of all organic compounds belongs to
(a) group 1
(b) group 14
(c) group 15
(d) group 16

Solution

(b) group 14 

All organic compounds contain carbon, which belongs to group 14.


10. Which of the following is the outermost shell for elements of period 2?
(a) K shell
(b) L shell
(c) M shell
(d) N shell

Solution

(b) L shell 

There are two shells K and L in period 18.


11. Which one of the following elements exhibit maximum number of valence eletrons ? 
(a) Na 
(b) Al 
(c) Si 
(d) P 

Solution

(d) P 

Electronic configuration of Na, Al, Si and P are 2,8 1, 2,8,3,2,8,4, and 2,8,5 respectively. Valence electrons in Na, Al, Si and P are 1,3,4 and 5.Therefore,Phas maximum number of valence electrons.


12. Which of the following gives the correct increasing order of the atomic radii of O, F and N ?
(a) O, F, N
(b) N, F, O
(c) O, N, F
(d) F, O, N

Solution

(d) F, O, N 

As one moves from left to right across a period, the atomic radius increases. N(7), O(8) and F(10) are in increasing order of atomic numbers.


13. Which among the following elements has the largest atomic radii ? 
(a) Na 
(b) Mg 
(c) K 
(d) Ca 

Solution

(c)  K 

K has largest atomic radii. The atomic radius decreases as one moves from left to right along a period. This happens because the nuclear charge increases, which tends to pull the electron closer to the nucleus thereby reducing the size of the atom.


14. Which of the following elements would lose an electron easily ? 
(a) Mg
(b) Na 
(c) K 
(d) Ca 

Solution

(b) Na 

Na and K belongs to the group I and Mg and Ca belong to group II. Na has 1 electron in its valence shell which can be lost easily.


15. Which of the following elements does not lose an electron easily ? 
(a) Na 
(b) F 
(c) Mg 
(d) Al 

Solution

(d) Al

Sodium, magnesium and aluminium have1, 2 and 3 electrons respectively in its outermost shell whereas fluorine has 7 electrons in its outermost shell. Therefore, fluorine does not lose electron easily.

 

16. Which of the following are the characteristics of isotopes of an element?
(i) Isotopes of an element have same atomic masses
(ii) Isotopes of an element have same atomic number
(iii) Isotopes of an element show same physical properties
(iv) Isotopes of an element show same chemical properties

(a) (i), (iii) and (iv)
(b) (ii), (iii) and (iv)
(c) (ii) and (iii)
(d) (ii) and (iv)

Solution

(d) (ii) and (iv) 

Elements with same atomic number but different atomic masses are known as isotopes. Isotopes have same chemical properties but different physical properties.


17. Arrange the following elements in the order of their decreasing metallic character Na, Si, Cl, Mg, Al
(a) Cl > Si >Al > Mg >Na
(b) Na >Mg >Al >Si > Cl
(c) Na > Al > Mg > Cl > Si
(d) Al > Na> Si > Ca> Mg

Solution

(b) Na >Mg >Al >Si > Cl

Sodium, magnesium, aluminium and chlorine have 1, 2, 3 and 7electrons in their valence shells respectively. Hence, sodium shows maximum metallic characters followed by magnessium, aluminium and chlorine shows non-metallic properties.


18. Arrange the following elements in the order of their increasing nonmetallic character Li, O, C, Be, F
(a) F < O < C < Be < Li
(b) Li < Be < C < O< F
(c) F < O < C < Be < Li
(d) F < O < Be < C < Li

Solution

(b) Li < Be < C < O< F

Li is on the left of in the 2nd period of modern periodic table followed by berrylium. Fluorine is at right next to Neon. Hence Fluorine shows maximum non-metallic characters followed by Oxygen, Berrylium, carbon and Lithium.


19.  What type of oxide would Eka– aluminium form?

(a) EO3
(b) E3O2
(c) E2O3
(d) EO

Solution

(c) E2 O3


20. Three elements B, Si and Ge are
(a) metals
(b) non-metals
(c) metalloids
(d) metal, non-metal and metalloid respectively

Solution

(c) metalloids


21. Which of the following elements will form an acidic oxide?
(a) An element with atomic number 7
(b) An element with atomic number 3
(c) An element with atomic number 12
(d) An element with atomic number 19

Solution

(a) An element with atomic number 7

The electronic configuration of an element with atomic number 7 is2,5. This means that the element can gain 3 electrons and thereby is an electronegative element. Therefore, it should be a non-metal and non-metals form acidic oxides.


22. The element with atomic number 14 is hard and forms acidic oxide and a covalent halide. To which of the following categories does the element belong?
(a) Metal
(b) Metalloid
(c) Non-metal
(d) Left-hand side element

Solution

(b) Metalloid 

Element with atomic no. 14 is Silicon and it is a metalloid. Silicon forms acidic oxide, there by behaving as a non-metal. It also forms covalent halides, thus acting as a metal as well.


23.  Which one of the following depict the correct representation of atomic radius(r) of an atom?

(a) (i) and (ii) 
(b) (ii) and (iii) 
(c) (iii) and (iv) 
(d) (i) and (iv) 

Solution

(b) (ii) and (iii) 

The distance between the nucleus and outermost orbital is known as the atomic radius. The atomic radius is shown clearly in images (ii) and (iii).


24. Which one of the following does not increase while moving down the group of the periodic table? (a) Atomic radius
(b) Metallic character
(c) Valence
(d) Number of shells in an element
Solution
(c) Valence
Valency remains thesame in a group.

25. On moving from left to right in a period in the periodic table, the size of the atom.
(a) increases
(b) decreases
(c) does not change appreciably
(d) first decreases and then increases
Solution
(b) decreases 

When one moves from left to right in a period then the atomic radius also decreases. Therefore, the size of the atom also decreases.


26. Which of the following set of elements is written in order of their increasing metallic character?
(a) Be Mg Ca
(b) Na Li K
(c) Mg Al Si
(d) C O N

Solution

(a) Be  Mg  Ca

As we move down the group, the metallic character increases. In the elements that belong to same group Be is at the top and Ca is at the bottom.


Short Answer Questions 

27. The three elements A, B and C with similar properties have atomic masses X, Y and Z respectively. The mass of Y is approximately equal to the average mass of X and Z. What is such an arrangement of elements called as? Give one example of such a set of elements.

Solution

The arrangement of these elements is known as Dobereiner’s triad. One example of such arrangement is, Lithium, Sodium and Potassium.


28. Elements have been arranged in the following sequence on the basis of their increasing atomic masses. F, Na, Mg, Al, Si, P, S, Cl, Ar, K (a) Pick two sets of elements which have similar properties. (b) The given sequence represents which law of classification of elements?

Solution

(a) The following set of elements have similar properties:

  1. F and Cl
  2. Na and K

(b) The given sequence represents Newland’s law of octaves.


29. Can the following groups of elements be classified as Dobereiner's triad ?
(a) Na, Si, Cl
(b) Be, Mg, Ca
Atomic mass of Be 9; Na 23; Mg 24; Si 28; Cl 35; Ca 40

Explain by giving reason. 

Solution

(a) The atomic mass of Silicon is the average of atomic masses of Sodium and Chlorine. But these elementsdo not have similar properties. This is the reason why they cannot be classified as Dobereiner’s triad.

(b) Yes, Be, Mg and Ca can be classified as Dobereiner’s triad because they have similar properties. Also the mass of magnesium (Mg) is roughly the average of the atomic mass of Be and Ca..


30. In Mendeleev’s Periodic Table the elements were arranged in the increasing order of their atomic masses. However, cobalt with atomic mass of 58.93 amu was placed before nickel having an atomic mass of 58.71 amu. Give reason for the same.

Solution

There are instances where elements with higher atomic mass are placed before the element with lower atomic mass in Mendeleev’s Period Table. This was done to ensure that elements with similar properties were included in the same group. As a result cobalt was placed before nickel despite of greater atomic number.


31. “Hydrogen occupies a unique position in Modern Periodic Table”. Justify the statement. 

Solution

Hydrogen occupies a unique position in Modern Periodic Table because of the following reasons.

  • Hydrogen has an outer electronic configuration similar to that of alkali metals. Hydrogen and alkali metals have one electron in their outermost shell.
  • Properties of hydrogen are also similar to that of halogens as electronic configurations of halogens and hydrogen are same.


32. Write the formulae of chlorides of Eka-silicon and Eka-aluminium, the elements predicted by Mendeleev. 

Solution

Chlorides of Eka - silicon: ECl4 
Chlorides of Eka - Aluminium : ECl3  


33. Three elements A, B and C have 3, 4 and 2 electrons respectively in their outermost shell. Give the group number to which they belong in the Modern Periodic Table. Also, give their valencies. 

Solution

  • A belongs to Group 13, B belongs to Group 14 and C belongs to Group 2.
  • Valency of A is 3, B is 4 and C is 2.


34. If an element X is placed in group 14, what will be the formula and the nature of bonding of its chloride ? 

Solution

As element X is placed in group 14,it has 4 electrons in its outermost orbit. The formula of its chloride will be ECl4.Theelement can form compound by sharing the valence electrons hence chemical bonding takes place.


35. Compare the radii of two species X and Y. Give reasons for your answer.
(a) X has 12 protons and 12 electrons
(b) Y has 12 protons and 10 electrons

Solution

From electron arrangement 

X - 2.8.2
Y - 2.8 
The atomic radius of Y will be smaller than that of Y as it has fewer energy levels.


36. Arrange the following elements in increasing order of their atomic radii.
(a) Li, Be, F, N
(b) Cl, At, Br I

Solution

Given elements are in the same group and are arranged from left to right. So, increasing order of their atomic radii
(a) Li>Be>F>N
(b) Cl>Br>I>At


37.  Identify and name the metals out of the following elements whose electronic configurations are given below.
(a) 2, 8, 2
(b) 2, 8, 1
(c) 2, 8, 7
(d) 2, 1

Solution

(a) Magnesium
(b) Sodium
(c) Chlorine
(d) Lithium


38. Write the formula of the product formed when the element A (atomic number 19) combines with the element B (atomic number 17). Draw its electronic dot structure. What is the nature of the bond formed?

Solution

Element A is K (Potassium). The electronic configuration of element A (atomic number 19) would be 2, 8, 8, 1.

Element B is Cl (Chlorine).The electronic configuration of element B (atomic number 17) would be 2, 8, 7. 

An ionic bond is usually formed when a metal and a non-metal combine. Metals have tendency to lose electrons to form cations whereas non-metals accept the electrons to form anions.

Dot structure:

Potassium and chlorine will combine to form potassium chloride (KCl).

The electron dot structure of KCl is as given below:


39. Arrange the following elements in the increasing order of their metallic character Mg, Ca, K, Ge, Ga 

Solution

Ge > Ga > Mg > Ca > K


40. Identify the elements with the following property and arrange them in increasing order of their reactivity
(a) An element which is a soft and reactive metal
(b) The metal which is an important constituent of limestone
(c) The metal which exists in liquid state at room temperature

Solution

(a) Na or K

(b) Ca 

(c) Hg The increasing order of reactivity of the elements is:
Hg < Ca < Na < K


41. Properties of the elements are given below. Where would you locate the following elements in the periodic table?
(a) A soft metal stored under kerosene
(b) An element with variable (more than one) valency stored under water.
(c) An element which is tetravalent and forms the basis of organic chemistry
(d) An element which is an inert gas with atomic number 2
(e) An element whose thin oxide layer is used to make other elements corrosion resistant by the process of “ anodising” . 

Solution

(a) Sodium (Na) Group 1 and Period 3 or Potassium (K) Group 1 and Period 4

(b) Phosphorus (P) Group 15 and Period 3

(c) Carbon (C) Group 14 and Period 2

(d) Helium (He) Group 18 and Period 1

(e) Aluminium (Al) Group 13 and Period 3


Long Answer Questions 

42. An element is placed in 2nd Group and 3rd Period of the Periodic Table, burns in presence of oxygen to form a basic oxide.
(a) Identify the element
(b) Write the electronic configuration
(c) Write the balanced equation when it burns in the presence of air
(d) Write a balanced equation when this oxide is dissolved in water (e) Draw the electron dot structure for the formation of this oxide

Solution

(a)  Element is Magnessium 
(b) Electronic Configuration  - 2, 8, 2
(c) 2Mg + O2 → 2MgO
(d) MgO + H2O → Mg(OH)2


43. An element X (atomic number 17) reacts with an element Y (atomic number 20) to form a divalent halide.
(a) Where in the periodic table are elements X and Y placed?
(b) Classify X and Y as metal (s), non-metal (s) or metalloid (s)
(c) What will be the nature of oxide of element Y? Identify the nature of bonding in the compound formed (d) Draw the electron dot structure of the divalent halide

Solution 

(a) X belongs to Group 17 and 3rd period and Y belongs to Group 2 and 4th period.

(b) X is anon-metal and Y is a metal.

(c) The oxides of element Y will be basic in nature. Ionic bonding is present in the oxide of element Y.
(d)

Electron dot-structure for calcium chloride


44. Atomic number of a few elements are given below 10, 20, 7, 14
(a) Identify the elements
(b) Identify the Group number of these elements in the Periodic Table
(c) Identify the Periods of these elements in the Periodic Table
(d) What would be the electronic configuration for each of these elements?
(e) Determine the valency of these elements

Solution

(a) Elements are Neon (10), Calcium (20), Nitrogen (7), Silicon (14).

(b) The elements belong to the following group:

  • Neon –18
  • Calcium –2
  • Nitrogen –15
  • Silicon -14

(c) The elements belong to the following period:

  • Neon –2
  • Calcium –4
  • Nitrogen –2
  • Silicon -3

(d) The electron configuration of the elements are as follows: 

  • Neon –2, 8
  • Calcium –2, 8, 8, 2
  • Nitrogen –2, 5
  • Silicon –2, 8, 4

(e) The valency of the elements is as follows:

  • Neon –0
  • Calcium –2
  • Nitrogen –3
  • Silicon –4


45. Complete the following cross word puzzle (figure 5.1)

Across : 
(i) An element with atomic number 12. 
(iii) Metal used in making cans and member of group 14.
(iv) A lustrous non - metal which has 7 electrons in its oiutermost shell. 

Down : 
(ii) Highly reactive and soft metal which imparts yellow colour when subjected to flame and is kept in kerosene.
(v) The first element of second Period
(vi) An element which is used in making fluorescent bulbs and is second member of Group 18 in the Modern Periodic Table
(vii) A radioactive element which is the last member of halogen family.
(viii) Metal which is an important constituent of steel and forms rust when exposed to moist air.
(ix) The first metalloid in Modern Periodic Table whose fibres are used in making bullet-proof vests 

Solution

Across
(1) Magnesium
(3) Tin
(4) Iodine
Down
(2) Sodium
(5) Lithium
(6) Neon
(7) Astatine
(8) Iron
(9) Boron

46. (a) In this ladder (Figure 5.2) symbols of elements are jumbled up. Rearrange these symbols of elements in the increasing order of their atomic number in the Periodic Table.
(b) Arrange them in the order of their group also.
Solution
(a) H, He, Li, Be, B, C, N, O, F, Ne, Mg, Al Si,P, S, Cl, Ar, K, Ca
b) Group 1:H, Li, Na, K
Group 2: Be, Mg, Ca
Group 13: B. Al
Group 14: C, Si
Group 15: N. P
Group 16: 0, S
Group 17: F. U
Group 18: He, Ne, Ar

47. Mendeleev ′ predicted the existence of certain elements not known at that time and named two of them as Eka-silicon and Eka-aluminium.
(a) Name the elements which have taken the place of these elements
(b) Mention the group and the period of these elements in the Modern Periodic Table.
(c) Classify these elements as metals, non-metals or metalloids
(d) How many valence electrons are present in each one of them?

Solution

(a) Eka-Silicon was replaced by germanium, Eka-aluminium was replaced by Gallium

(b) Germanium-Group 14 Period 5

Gallium-Group 13 Period 5

(c) Germanium is a metalloid and Gallium is a metal.

(d) Germanium has 4 electron, Gallium has 3 valence electrons.


48. (a) Electropositive nature of the element(s) increases down the group and decreases across the period
(b) Electronegativity of the element decreases down the group and increases across the period
(c) Atomic size increases down the group and decreases across a period (left to right)
(d) Metallic character increases down the group and decreases across a period.
On the basis of the above trends of the Periodic Table, answer the following about the elements with atomic numbers 3 to 9.
(a) Name the most electropositive element among them
(b) Name the most electronegative element
(c) Name the element with smallest atomic size
(d) Name the element which is a metalloid
(e) Name the element which shows maximum valency.
Solution
(a) Lithium is the most electropositive element.
(b) Fluorine is the most electronegative element.
(c) Fluorine has thesmallest atomic size among the given elements.
(d) Boronis a metalloid.
(e) Carbon shows maximum valency.

49. An element X which is a yellow solid at room temperature shows catenation and allotropy. X forms two oxides which are also formed during the thermal decomposition of ferrous sulphate crystals and are the major air pollutants.
(a) Identify the element X
(b) Write the electronic configuration of X
(c) Write the balanced chemical equation for the thermal decomposition of ferrous sulphate crystals?
(d) What would be the nature (acidic/ basic) of oxides formed?
(e) Locate the position of the element in the Modern Periodic Table
Solution
(a) Element X is Sulphur 
(b) 2, 8, 6
(c) 2FeSO4 → Fe2O3 + SO2 + SO3
(d) Sulphur oxides are acidic in nature
(e) Group 16 Period 3

50. An element X of group 15 exists as diatomic molecule and combines with hydrogen at 773 K in presence of the catalyst to form a compound, ammonia which has a characteristic pungent smell. (a) Identify the element X. How many valence electrons does it have?
(b) Draw the electron dot structure of the diatomic molecule of X. What type of bond is formed in it?
(c) Draw the electron dot structure for ammonia and what type of bond is formed in it?
Solution
(a) Answer is Nitrogen and it has 5 electrons in its outermost shell. 
(b)
(c) Ammonia forms covalent bonding

51. Which group of elements could be placed in Mendeleev's ′ Periodic Table without disturbing the original order? Give reason.
Solution
According to Mendeleev’s periodic table, the properties of elements are the periodic function of their atomic masses. There is a periodic recurrence of elements with similar physical and chemical properties. Noble gas being inert could be placed in a separate group without disturbing the original order.

52. Give an account of the process adopted by Mendeleev ′ for the classification of elements. How did he arrive at “Periodic Law”?
Solution
The number of known elements at Mendeleev’s time was 63. He examined the correlation between chemical properties and atomic masses of elements. He studied the compounds which the known elements formed with hydrogen and oxygen. Hydrogen and oxygen were selected by Mendeleev because these elements form compound with most of the other elements. Mendeleev then made 63 cards and wrote the name of an element on each card: along with the chemical properties of a particular element. He then pinned those cards on a wall. He observed that most of the elements can be arranged in periodic table in increasing order of their atomic masses. That is how Mendeleev arrived at “Periodic law”. Mendeleev’s Periodic Law states that properties of elements are periodic function of their atomic masses.

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