Class 10 Science Chapter 5 Board Questions

Class 10 Science Chapter 5 Board Questions of Periodic Classification of elements. Sets of previous years CBSE Board questions, last ten years, last 5 years sample papers and board exams questions with complete explanation and answers are are given below for the academic session 2020-2021.

Class 10 Science Chapter 5 Board Questions Answers

Class: 10Science
Chapter 5: Periodic Classification of elementsBoard Questions with Answers

Class 10 Science Chapter 5 CBSE Board Questions

Class 10 Science Chapter 5 Board Questions with answers are given below in the form of sets of questions. There are the questions of 1 Mark, 2 Marks, 3 Marks and 5 Marks. The answer of each question is given just below the questions. Practicing these questions makes a student confident in school test as well as CBSE Board Exams.

10th Science Chapter 5 Board Questions Set – 1 (1 Mark)

Element A, B, C and D have atomic numbers 1,8,11, and 19 respectively. Choose the odd element and give reason for your answer. [CBSE 2011]

Element B is Odd element.
Elements A, C and D belong to group 1 because they have 1 electron in the outermost shell.
Elements B does not belong to this group at these 6 electrons in the valence shell.

Size of sodium atom is bigger than that of hydrogen atom. Why? [CBSE 2012]

Hydrogen atom contains one shell while sodium contains three shells. Atomic size increases with the number of shells.

Name the elements which has twice as many electrons it its second shell as in its first shell. Write its electronic configuration also. [CBSE 2012]

The element is carbon.
It has a total number of 6 electrons 2 in the first shell and 4 in the second shell.
Electronic configuration:
K = 2, L = 4

Mention the common name given to the following elements: Boron, Silicon, Germanium, Arsenic, Antimony State one property that justifies their names. [CBSE 2012]

They are called metalloids. They show the properties of metal and non-metal.

Write two reasons for late discovery noble gases? [CBSE 2013]

1. They are present in very low concentration.
2. They have no tendency to react.

One mark questions can be answered in one sentence or one word. Hints for answers are given to help the students. You can make your answers from the hints given in the form of answers.

10th Science Chapter 5 Board Questions Set – 2 (1 Mark)

Write the valency and usual number of electrons of group 18 of the periodic table. [CBSE 2013]

Valency = 0
Number of electrons = 8

How many horizontal rows are there in the Modern Periodic Table and what are they called? [CBSE 2013]

There are seven Horizontal rows.
They are called periods.

Write the formula of chloride of Eka silicon and Eka Aluminium that elements predicted by Mendeleev? [CBSE 2012]

GeCl2 and GaCl2.

If an element X is placed in group 14, what will be the formula and nature of bonding of its chloride. [CBSE 2014]

Formula of its chloride = XCl4
Nature of bonding in its chloride = Covalent.

State one region for placing Mg and Ca in the same group of periodic table? [CBSE 2014]

This is because both Mg and Ca contain two electrons in the outermost shell.

10th Science Chapter 5 Board Questions Set – 3 (1 Mark)

Why does silicon has valency 4? [CBSE 2013]

Silicon has electronic configuration 2,8.4. As there are four electrons in the outermost shell its valency is 4.

Can the following groups of elements be classified as Dobereiner’s Triads? Na, Si, Cl. [CBSE 2012]

No, because the elements do not have similar chemical properties although the atomic mass of Si is the average of atomic mass of Na and Cl.

Arrange the following elements in increasing order of their atomic radii: Cl, At, Br, I. [CBSE 2012]

Cl< Br< I< At

What are the two reason for the late discovery of Noble gases? [CBSE 2013]

(i) Noble gas are inert.
(ii) These are present in nature in minutes’ amount.

State modern periodic law. Where are (i) metals, (ii) non-metals (iii) metalloids located in the periodic table? [CBSE 2011]

The physical and chemical properties of elements are the periodic function of their atomic numbers.
(i) Metals are located toward left in the periodic table.
(ii) Non-metals are located toward right in the periodic table.
(iii) Metalloids are located in the middle toward right in the periodic table.

The Position of Hydrogen and Isotopes

Hydrogen is placed at the top of group IA.
Isotopes of the same element are placed in the same slot.

10th Science Chapter 5 Board Questions Set – 4 (3 Marks)
Inert gases are placed in a separate group in the modern periodic table. (a) State the group number (b) How many valence electrons do most of these gases have? (c) Why are they unreactive? (d) Name any two inert gases. [CBSE 2012]

(a) Group number for inert gases in the Periodic Table is 18.
(b) Except helium these gases have 8 valence electrons.
(c) Their octet is already complete. Therefore, they have no tendency to react.
(d) (i) Neon
(ii) Argon.

The elements of the second period of the periodic table are given below: Li, Be, B, C, N, O, F, Ne. (a) Give reason to explain why atomic radius decreases from Li to F. (b) Identifying the most metallic and non-metallic elements. (c) How does valency change from Li to Ne? [CBSE 2011]

(a) Nuclear charge increases as we move from Li to Ne. Increased nuclear charges pulls the electron closer to the nucleus. Therefore, atomic radius decreases from Li to F.
(b) As we move from left to right the number of electrons in the outermost orbit increases. Thus tendency to lose electrons decreases from Li to Ne. Therefore, Li is most metallic and F is most non-metallic, Ne being inert.
(c) Valency increases from 1 to 4 for Li, Be, B and C and
Valency of N =8-5=3
Valency of O =8-6=2
Valency of F = 8-7=1
Valency of Ne = 8-8=0

An element A reacts with oxygen to form A2O. (i) State the number of electrons in the outermost orbit A. (ii) To which group of the periodic table does A belong? (iii) State whether A is a metal or a non-metal. [CBSE 2012]

(i) As the valency of oxygen is 2 the valency of A must be 1 in order to obtain the compound A2O. Therefore, the number of electrons in the outermost orbit of A is 1.
(ii) A belongs to group 1 of the periodic table. Elements of this group have 1 electron in the outermost orbit.
(iii) A is a metal. Elements of group 1 having 1 electron in the outermost orbit have a tendency to lose electrons.

Calcium magnesium and strontium have been put together in the same group of Periodic table on the basis of their similar chemical properties. (i) Mention those properties. (ii) Out of three elements which one will have atoms of biggest size and why? (iii) Which is the first member of this group? [CBSE 2012]

(i) (a)They shows metallic properties.
(b) Their oxide are basic I nature.
(ii) Strontium has atom of biggest size. As we move down in the group atom size increases.
(iii) Beryllium.

The Modern Periodic Law

The physical and chemical properties of elements are the periodic function of their atomic numbers. The modern periodic table is called long forms of the periodic table.

10th Science Chapter 5 Board Questions Set – 5 (3 Marks)
Four elements P, Q, R and S have atomic numbers, 12, 13, 14 and 15 respectively. Answer the following question giving reason: (i) What is the Valency of Q? (ii) Classifying these elements as metals and non-metals. (iii) Which of these elements will form the most basic oxide? [CBSE 2013]

(i) Q atomic number 13. Thus it has electronic configuration 2,8,3. Therefore its, valency is 3.
(ii) Element P and Q have 2and 3 electron respectively in the valence shell. They will have a tendency to lose electrons respectively and are therefore metals. Element R and S have 4 and 5 electrons respectively in their valence shell. They will have tendency to gain or share the electron to complete the octet. Therefore, R and S are non-metals.
(iii) P will form the most basic oxide. Only the metals form basic oxide and P is more metallic than Q.

Give one example of each: (a) Metals having valency 2. (b) Non-metal having valency 2. (c) Elements with three shells, having 4 electrons in the outermost shell. [CBSE 2014]

(a) Magnesium has a valency of 2.
(b) Sulphur has a valency 2.
(c) Silicon gas three shells having 4 electrons in the outermost shell (2, 8, 4).

How do the following traits change in a period from left to right in the periodic table? (a) Atomic size (b) Valency (c) Metallic character. [CBSE 2014]

(a) Atomic size decreases as we move from left to right in the periodic table. This is because the electrons are added to the same shell. Because of increased attraction between the nucleus and the electrons, atomic size decreases.
(b) Valency increases as we move from left to right to some point after which it decreases. Valency depends upon the number the number of electrons which an atom can lose, gain or share with other atoms.
(c) Metallic character decreases as we move left to right in the periodic table. Metallic character means tendency to lose electrons increases. Therefore, elements have smaller and smaller tendency to lose electrons.

Two elements X and Y belongs to the second group of the periodic table X has 2 shells and Y has 3 shell in it. (a) Which of these more metallic in nature and why? (b) What is the formula of the chloride of X and Sulphide of Y? (c) Is the valency of X same as that of Y or different? Why? [CBSE 2014]

(a) Y is more metallic in nature. As we move down the group the valence electrons get farther from the nucleus. The hold of the nucleus on the valence electron decreases down the group.
(b) XCl2 and YS
(c)X has the same valency as Y which is equal to 2. This is because both have 2 electrons.

How many groups and periods are there in the modern periodic table? How do the atomic size and metallic character of elements vary as we move: (a) down a group and (b) from left to right in period. [CBSE 2015]

There are 18 group and 7 periods in the modern periodic table.
(a) On moving down a groups the atomic size increases and metallic character also increases.
(b) On moving from left to right in a period, the atomic size decreases and the metallic character also decreases.

10th Science Chapter 5 Board Questions Set – 6 (3 Marks)
From the following elements: Be(4), F(9), K(19), Ca(20). (i) select the elements having one electron in the outermost shell. (ii) two electron of same group. Write the formula of and mention the nature of the compound formed by the union of 19K and element X (2,8,7). [CBSE 2015]

(i) 19K has one electron in the outermost shell. It has the electronic configuration: 2, 8, 8, 1.
(ii) 4Be and 20Ca belong to group 2.
Both of them have two electrons in the outermost shell and therefore belong to group 2.
Formula of the compound formed by the union of 19K, and X (2, 8, 2) is: KX.
Nature of the compound will be ionic because K(2,8,8,1) will donate one electron to X. This will complete the octet of both.

Calcium is an element with atomic number 20. Stating reason answer each of the following questions: (i) Is calcium a metal or non-metal? (ii) Will its atomic radius be large or smaller than that of potassium with atomic number 19? (iii) Write the formula of its oxide. [CBSE 2016]

(i) Calcium is a metal.
The oxide of calcium CaO is a basic oxide because it dissolves in water to give a base.
2Ca + O2 → 2CaO
CaO + H2O → Ca(OH)2
(ii) Atomic radius of Ca is smaller than that of K. This is because, the next electron enters the same orbit as that of the last electron of K.
Electronic configuration of K:2, 8, 8, 1.
Electronic configuration of Ca: 2,8,8,2.
And because of the increased nuclear charge the electron in the last orbit are attracted with a greater force resulting in the decrease of atomic radius.
(iii) CaO is the formula of oxide of calcium.

Why is atomic number of an element more important to a chemist than its atomic mass? [CBSE 2011]

The properties of elements depends upon the number of electrons present in the valence shell which are related to atomic number. Thus properties of different elements can be compared if we know their atomic number. On the other hand, atomic mass can in no way determine the chemical properties of elements, because it does not vary regularly with gradation in the chemical properties of elements.

Two elements X and Y belong to groups 1 and 3 respectively in the same period compare these with respect to their (a) metallic character (b) size of the atoms (c) formulae of their oxides and chlorides. [CBSE 2012]

(a) Metallic character decreases from X to Y.
(b) Elements X is bigger than Y.
(c) X2O, XC, X2O3, YCl3.

Part of the periodic table is given below where atomic numbers of elements are given in the parenthesis. Li (3) and Be (4), Na (11) and Mg (12), K(19) and Ca (20), Rb (37) and Sr (38). (i) Give the electronic configuration of K. (ii) Predict the number of valence electrons in the atom of Ca. (iii) What is the number of shells in the atom of Na? (iv) Arrange Be, Mg, Ca, Sr in the increasing order of the size of their respective atoms. (v) Predict whether Rb is a metal or non-metal. (vi) Out of Na, Li, Be and Mg which one has biggest atom in size? [CBSE 2013]

(i) Electronic configuration of K= 2, 8, 8, 1.
(ii) Valence electrons in the atom of Ca = 2.
(iii) Number of shells in the atom of Na = 3.
(iv) Be < Mg < Ca < Sr. (v) Rb is a metal. (vi) Na has biggest atom in size out of Na, Li, Be, Mg.

Most of the important questions from CBSE Board examination are included here in the form of sets of 1 mark, 3 marks and 5 marks questions. If still there is any questions to be asked, please visit to Discussion Forum.

10th Science Chapter 5 Board Questions Set – 7 (5 Marks)
(i) Why do we classify elements? (ii) What are the two criteria used in the development of Modern Periodic Table? (iii) State the position of (a) metals (b) non-metals and (c) metalloids in the Periodic Table. (iv) Would you place two isotopes of Cl-35 and Cl-37 in different slots of the Periodic Table because of their chemical properties are same? Justify your answer. [CBSE 2011]

(i) We classify elements in order to study their properties properly by grouping together elements having similar properties.
(ii) The two criteria used in the development of Modern Periodic Table are atomic number of electrons in the outermost shell.
(iii) Metals are located on the left hand side of the periodic table while non-metals are located on the right hand side of the table. Metalloids are located in between the two.
(iv) The two isotopes of chlorine would be placed at the same position because the valence electrons and chemical properties are the same for the two isotopes.

Consider the following elements: 20A, 8B, 18C, 16D, 4E, 2F. Answer the following giving reason: Which of the above elements you would expect to be (i) very stable. (ii) in group 2 of the periodic table. (iii) in a group 16 of the periodic table. (iv) What type of bond will be formed when the elements A react with B? Explain. [CBSE 2013]

(i) 2F and 18C are very stable elements because they contain 2 and 8 electrons in the outermost shell.
(ii) Elements 4E and 20A are in group of 2 of the periodic table because E has the electronic configuration 2, 2 and A has electronic configuration 2, 8, 8, 2. Both have 2 electrons in the outermost shell.
(iii) 8B and 16D occupy group 16 of the periodic table. Both contain 6 electrons in the outermost shell.
(iv) A and B will react to form AB with an ionic bond. A will donate two electrons to B to form the compound.

The atomic number of Cl is 17. On the basis of this information answer the questions the follow: (a) Write the electronic configuration of Cl. (b) Find the valency. (c) To which group does it belong (d) Identify the type of ions it will form. (e) Write down the formula of the compound it forms with others elements. [CBSE 2014, 2017]

(a) Electronic configuration of Cl is 2,8,7.
(b) Valency of Cl is 1as it requires only one electron to complete its octet.
(c) It belong to group 17 of the modern periodic table.
(d) It will form an anion by gaining one electron.
(e) It form HCl with H and NaCl with Na.

(a) The Modern Periodic Table has been involved through the early attempts of Dobereiner, Newland and Mendeleev. List one advantages and one limitation of all three attempts. (b) Name the scientist who first of all showed that atomic number of an element is a more fundamental property than its atomic mass. (c) State Modern Periodic Law. [CBSE 2016]

(a) Dobereiner attempt:
Advantage: The atomic mass of the middle element of the triads was the mean of the other two elements.
Limitation: Dobereiner could identify only three triads.
Newland Attempt:
Advantage: Every eighth element has properties similar to that of the first. Sodium is the eight element after lithium. These two elements have similar properties.
Limitation: No fixed position in the periodic table could be given to hydrogen by Mandeleev classification.
(b) Henry Mosely.
(c) Properties of elements are a periodic function of their atomic number.

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