NCERT Exemplar Solutions Class 10 Science Periodic Classification of Elements

Multiple Choice Questions.....................

Question 1: Up to which element, the Law of Octaves was found to be applicable

(a) Oxygen

(b) Calcium

(c) Cobalt

(d) Potassium 

Solution 1: (b) Calcium 

The law of octaves was extended to elements with atomic masses up to 40 da, which includes Calcium. Every eighth element, after calcium, has properties that are similar to those of the first.

Question 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 2: (c) increasing atomic masses

According to Mendeleev’s ′ Periodic Law, the elements were arranged in the periodic table in the order of increasing atomic masses.

Question 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 periodic table later

(a) Germanium

(b) Chlorine

(c) Oxygen

(d) Silicon 

Solution 3: (a) Germanium

Unnamed elements were given the names EKA- Boron, EKA- Aluminum, and EKA Silicon by Mendeleev, which were later replaced by Scandium, Gallium, and Germanium.

Question 4:  Which of the following statement (s) about the Modern Periodic Table are incorrect

(i) The elements in the Modern Periodic Table are arranged based on their decreasing atomic number

(ii) The elements in the Modern Periodic Table are arranged based on 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 based on their increasing atomic number

(a) (i) only

(b) (i), (ii) and (iii)

(c) (i), (ii) and (iv)

(d) (iv) only 

Solution 4:  (b) (i), (ii) and (iii)

Option I is incorrect since elements in the Modern Periodic Table are ordered by increasing atomic number. Option ii) is incorrect since atomic mass is not a criterion in the current periodic table. Option iii) is incorrect since isotopes have the same place in the periodic table.

Question 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 5:  (c) It has 18 vertical columns known as Groups

There are 18 groups and 7 cycles in the modern periodic table. Columns are referred to as classes, and rows are referred to as intervals.

Question 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 6: (b) B, C, D

The first period includes elements with atomic numbers, while the second period includes elements B, C, and D.

Question 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 7:  (c) A and C

A and C are fluorine, and chlorine is a member of the same family as fluorine.

Question 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 8:  (c) Group 18

The outermost shells of group 18 are absolutely filled, so any element with an electronic configuration belongs to this group.

Question 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 9: (b) group 14

All organic compounds in group 14 contain carbon, which is an important component.

Question 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 10:  (b) L shell

There are two shells K and L in period 18.

Question 11:  Which one of the following elements exhibit a maximum number of valence electrons?

(a) Na

(b) Al

(c) Si

(d) P 

Solution 11: (d) P

Na, Al, Si, and P have electronic configurations of 2,8,1, 2,8,3,2,8,4, and 2,8,5 respectively. In Na, Al, Si, and P, the valence electrons are 1,3,4, and 5. As a result, phosphorus has the most valence electrons.

Question 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 12: (d) F, O, N

As you move from left to right over a time, the atomic radius increases. The atomic numbers (N7), O(8), and F(10) are in ascending order.

Question 13: Which among the following elements has the largest atomic radii?

(a) Na

(b) Mg

(c) K

(d) Ca 

Solution 13:  (c) K

Since atomic radii decrease from left to right along a time, K has the largest atomic radii. This is due to an increase in nuclear charge, which appears to pull the electron closer to the nucleus, shrinking the atom's size. As a result, K has the most atomic radii.

Question 14:  Which of the following elements would lose an electron easily?

(a) Mg

(b) Na

(c) K

(d) Ca 

Solution 14: (b) Na

Magnesium and Calcium belong to group ii, while Na and K belong to group I. Sodium has a single electron in its valence ring, which is quickly lost.

Question 15: Which of the following elements does not lose an electron easily?

(a) Na

(b) F

(c) Mg

(d) Al 

Solution 15: Fluorine has seven electrons in its outermost shell, while sodium has one, magnesium has two, and aluminium has three. Fluorine does not lose electrons quickly.

Question 16: Which of the following are the characteristics of isotopes of an element?

(i) Isotopes of an element have the same atomic masses

(ii) Isotopes of an element have the same atomic number

(iii) Isotopes of an element show the same physical properties

(iv) Isotopes of an element show the same chemical properties

(a) (i), (iii) and (iv)

(b) (ii), (iii) and (iv)

(c) (ii) and (iii)

(d) (ii) and (iv) 

Solution 16:  (d) (ii) and (iv) 

Isotopes are elements of the same atomic number but different atomic masses. Isotopes have the same chemical properties as each other, but their physical properties vary.

Question 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 17:  (b) Na >Mg >Al >Si > Cl 

In its valence shells, sodium has one electron, magnesium has two, aluminium has three, and chlorine has seven. Consequently Sodium has the most metallic properties, followed by magnesium, aluminium, and chlorine, which have non-metallic characteristics.

Question 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 18:  (b) Li < Be < C < O< F

Li is on the left of the modern periodic table's second period, followed by berrylium. Fluorine is right next to Neon in the periodic table. As a result, fluorine has the most nonmetallic properties, followed by oxygen, berylium, carbon, and lithium.

Question 19:  What type of oxide would Eka– aluminium form?

(a) EO₃

(b) E₃ O₂

(c) E₂ O₃

(d) EO 

Solution 19: (c) E₂O₃ 

E₂O₃ oxide would Eka– aluminium forms.

Question 20:  Three elements B, Si and Ge are

(a) metals

(b) non-metals

(c) metalloids

(d) metal, non-metal and metalloid respectively

Solution 20: (c) metalloids 

Three elements B, Si and Ge are metalloids. 

Question 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 21: (a) An element with atomic number 7 

The electron configuration of the element with atomic number 7 is 2,5, which means it can gain three electrons and is an electronegative element. It should be non-metallic, as metals produce acidic oxide. 

Question 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 22:  (b) Metalloid 

Silicon is a metalloid with an atomic number of 14. It forms an acidic oxide, which makes it a non-metal, and a covalent halide, which makes it a metal. 

Question 23:  Which one of the following depicts the correct representation of the atomic radius(r) of an atom?

 (a) (i) and (ii)

(b) (ii) and (iii)

(c) (iii) and (iv)

(d) (i) and (iv)  

Solution 23:  (b) (ii) and (iii)

The atomic radius, which is the distance between the nucleus and the outermost orbital, is clearly seen in images ii) and iii), but not in images I and iv).

Question 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 24:  (c) Valence

In a group, the value remains constant.

Question 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 25: (b) decreases

As we shift from left to right in a time, the atomic radius decreases, and the size of the atom decreases as well.

Question 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 26:  (a) Be Mg Ca

As we progress through the party, the metallic character becomes more prominent. Berrylium is at the top of the list of elements that belong to the same group, and Calcium is at the bottom.

Short Answer Questions......................................

Question 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 27:  Triads are a form of elemental arrangement. A triad is formed by the elements lithium, sodium, and potassium. Their respective atomic masses are 6.9, 23.0, and 39.0. The atomic mass of Na is roughly equal to the average mass of Li and K.

Question 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 28:

(a) Metals include sodium, magnesium, aluminium, and potassium. Halogens include F and Cl. There are two sets of elements as a result of this.

(b) Mendeleev's law of periodicity is represented by the given set.

Question 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 29:  Since the atomic mass of Silicon is the average of the atomic masses of Sodium and Chlorine, they may not have the same properties as Dobereiner's triad.

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

Solution 30:   There are instances in Mendeleev's Periodic Table where elements with higher atomic masses are grouped before elements with lower atomic masses. This was achieved so that elements with similar properties can be grouped together. Despite the fact that Cobalt has a higher atomic number than Nickel, it was put first.

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

Solution 31:   Because of the following factors, hydrogen has a special role in the Modern Periodic Table.

1. Since both hydrogen and alkali metals have one electron in their outermost shell, their outer electronic configurations are identical.

2. Since the electronic structures of halogens and hydrogen are the same, their properties are identical.

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

Solution 32:

Eka-silicon chlorides: ECl₄

Eka-Aluminium Chlorides: ECL₃  

Question 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 33:   A is a member of Group 13, A is a member of Group 14, and C is a member of Group 2. A has a value of 3, B has a value of 4, and C has a value of 2.

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

Solution 34:   When an element X is put in group 14, its outermost orbit has four electrons. Its chloride formula is ECl₄. Chemical bonding occurs when two elements share electrons and form a compound.

Question 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 35:  From electron arrangement:

(a) X -2, 8, 2

(b) Y -2, 8

Since Y has less energy levels than X, its atomic radius would be smaller.

Question 36:  Arrange the following elements in increasing order of their atomic radii.

(a) Li, Be, F, N

(b) Cl, At, Br I 

Solution 36:  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

Question 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 37:

(a) Magnesium

(b) Sodium

(c) Chlorine

(d) Lithium

Question 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 38:

The letter K stands for the element A. (Potassium).

Element A (atomic number 19) has an electronic configuration of 2, 8, 8, 1. It must be a metal because it only has one valence electron. As a result, potassium.

Cl is the name of the element B. (Chlorine).

Element B (atomic number 17) has an electronic configuration of 2, 8, 7. It must be a non-metal since it has seven valence electrons. It's chlorine, then.

An ionic bond is formed when a metal and a non-metal interact. Non-metals can take electrons and form anions, whereas metals lose electrons and form cations.

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

Solution 39:  Arrangment of these elements in the increasing order of their metallic character Mg, Ca, K, Ge, Ga

Ge > Ga > Mg > Ca > K

Question 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 a liquid state at room temperature 

Solution 40:

(a) Sodium is the element which is a soft and reactive metal.

(b) Calcium is the metal which is an important constituent of limestone.

(c) Mercury is the metal which exists in a liquid state at room temperature.

Question 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 underwater.

(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 41:

(a) Sodium is the soft metal stored under kerosene and is located in Group 1 Period 3.

(b) Phosphorus is the element with variable (more than one) valency stored underwater and is located in Group 15 Period 3.

(c) Carbon is the element which is tetravalent and forms the basis of organic chemistry and located in Group 14 Period 2.

(d) Helium is the element which is an inert gas with atomic number 2 and is located in Group 18 Period 1.

(e) Aluminium is the element whose thin oxide layer is used to make other elements corrosion-resistant by the process of “ anodising” and is located in Group 13 Period 3.

Long Answer Questions......................................

Question 42:  An element is placed in 2^nd Group and 3^rd 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 42:

(a) Element is Magnesium.

(b) Electronic Configuration of magnesium is 2,8,2.

(c) 2Mg + O₂ → 2MgO.

(d) MgO + H₂O → Mg(OH)_2.

Question 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 43:

(a) X belongs to group 17 and is in period 3, while Y belongs to group 2 and is in period 4.

(b) Metal is Y and non-metal is X.

(c) In nature, Y Oxide will be simple. Ionic bond forms a compound.

Question 44:  Atomic numbers 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 44:

(a) Elements are:

Neon is the element with atomic number 10.

Calcium is the element with atomic number 20.

Nitrogen is the element with atomic number 7.

Silicon is the element with atomic number 14. 

(b) Group 18 is made up of neon, group 2 is made up of calcium, group 7 is made up of nitrogen, and group 14 is made up of silicon. 

(c) Period 2 includes nitrogen and neon, while Period 3 includes calcium and silicon. 

Question 45:  Complete the following crossword puzzle:

Across:

(1) An element with atomic number 12.

(3) Metal used in making cans and member of Group 14.

(4) A lustrous non-metal which has 7 electrons in its outermost shell.

Down:

(2) Highly reactive and soft metal which imparts yellow colour when subjected to flame and is kept in kerosene.

(5) The first element of the second Period

(6) An element which is used in making fluorescent bulbs and is the second member of Group 18 in the Modern Periodic Table

(7) A radioactive element which is the last member of the halogen family.

(8) Metal which is an important constituent of steel and forms rust when exposed to moist air.

(9) The first metalloid in Modern Periodic Table whose fibres are used in making bullet-proof vests

Solution 45:

Across:

1) Magnesium

3) Tin

4) Iodine 

Down:

2) Sodium

5) Lithium

6) Neon

7) Astatine

8) Iron

9) Boron

Question 46:  

(a) In this ladder 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 46:

a) H, He, Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K, Ca

b)

H, Li, Na, K of Group 1

Be, Mg, Ca of Group 2

B, Al of Group 13

C, Si of Group 14

N. P of Group 15

O, S of Group 16

F, U of Group 17

He, Ne, Ar of Group 18

Question 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 47:

a) Eka-silicon was substituted with germanium, and Eka-aluminium with gallium.

b) Germanium is of Group 14 and Period 5.

Gallium is of Group 13 and Period 5.

c) Gallium is a metal whereas Germanium is a metalloid.

d) 4 electrons are there in Germanium and Gallium has 3 valence electrons.

Question 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.

Based on 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 the smallest atomic size

(d) Name the element which is a metalloid

(e) Name the element which shows maximum valency. 

Solution 48:

(a) The most electropositive element is lithium.

(b) Fluorine is the most electronegative element in the periodic table.

(c)  Among the given elements, fluorine has the smallest atomic size.

(d) Boron is the element which is a metalloid.

(e) The element with the most valency is carbon.

Question 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 49:

(a) Sulphur is element X.

(b) Electronic configuration of sulphur is 2,8,6.

(c) 2FeSO₄ → Fe₂O₃ + SO₂ + SO₃

(d) Sulphur oxides are naturally acidic.

(e) Sulphur is located in Group 16 and Period 3.

Question 50:  An element X of group 15 exists as a 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 50:

(a) Element X is Nitrogen, and its outermost shell has 5 electrons.

Question 51:  Which group of elements could be placed in Mendeleev’s ′ Periodic Table without disturbing the original order? Give reason. 

Solution 51:

Mendeleev's Periodic Table could be filled with inert gases without disrupting the original order.

Noble gases, such as helium, existed before Mendeleev. Various scientists had described neon and argon. However, these gases were not classified as noble gases until much later than Mendeleev's discovery.

Because these were the only known elements at the time, Mendeleev used 63 elements in his periodic table. He did, however, take the risk of leaving gaps in his periodic table. He expected that in the future, more elements will be found.

The Periodic Table of Mendeleev was the first attempt to classify elements based on their chemical properties. This is the primary explanation for the ease with which new elements could be added to Mendeleev's Periodic Table without disrupting the original order.

Question 52:  Give an account of the process adopted by Mendeleev ′ for the classification of elements. How did he arrive at “Periodic Law”?

Solution 52:   Only 63 elements were known during Mendeleev's period. Mendeleev studied the relationship between chemical properties and element atomic masses. For this, he focused on compounds formed by elements containing hydrogen and oxygen. He chose hydrogen and oxygen because they form compounds with the majority of the other elements.