CBSE Class 10 Chemistry Periodic Classification Of Elements Worksheet Set A

Multiple choice questions 

Question : The properties of Eka-aluminium predicted by Mendeleev are the same as the properties of later discovered element:
(a) Scandium
(b) Germanium
(c) Gallium
(d) Aluminium
Answer : C

Question : The arrangement of elements in the Modem Periodic Table is based on their
(a) increasing atomic mass in the period
(b) increasing atomic number in the horizontal rows
(c) increasing atomic number in the vertical columns
(d) increasing atomic mass in the group
Answer : B

Question : Element ‘X’ forms a chloride with the formula XCl2, which is a solid with high melting point. X would most likely be in the same group of the periodic table as:
(a) Si
(b) Mg
(c) Al
(d) Na
Answer : B

Question : What is the atomic number of element of period 3 and group 17 of the Periodic Table?
(a) 10
(b) 4
(c) 17
(d) 21
Answer : C

Question : An element X from group 2 of the Periodic Table reacts with Y from group 17 to form a compound. Give the formula of the compound.
(a) XY2
(b) XY
(c) X2Y
(d) (XY)2
Answer : A

Question : A metal ‘M’ is in the first group of the Periodic Table. What will be the formula of its oxide? (a) MO
(b) M₂O
(c) M₂O₃
(d) MO₂
Answer : B

Question : An element X has mass number 40 and contains 21 neutrons in its atom. To which group of the Periodic Table does it belong?
(a) Group 1
(b) Group 4
(c) Group 2
(d) Group 3
Answer : A

Question : What is the other name for group 18th elements?
(a) Noble gases
(b) Alkali metals
(c) Alkali earth metals
(d) Halogens
Answer : A

Question : The atom of an element has electronic configuration 2, 8, 7. To which of the following elements would it be chemically similar?
(a) 7N
(b) 15P
(c) 11Na
(d) 9F
Answer : D

Case study questions

Modern periodic table has 18 vertical columns known as groups and 7 horizontal rows known as periods. First period contains 2 elements second and third period contain 8 elements. 4th and 5th period contains 18 elements and 6th and 7th period contains 32 elements. The graph is plotted between atomic number and atomic radius of group 17 and group 1 elements.

Question. What happens to atomic radii in a group from top to bottom?
(a) Increases
(b) Decreases
(c) First decreases then increases
(d) Number of shells remains the same
Answer : A

Question. Which group elements will have largest atomic size?
(a) Group 1
(b) Group 2
(c) Group 3
(d) Group 18
Answer : A

Question. Which element in group 17 has smallest size?
(a) Flourine
(b) Bromine
(c) Chlorine
(d) Iodine
Answer : A

Question. Which group elements will gain electrons to form negative ions?
(a) Group 1
(b) Group 2
(c) Group 17
(d) Group 18
Answer : C

Question. Atomic size decreases from left to right in a period because
(a) Effective nuclear charge increases
(b) Number of shells remains the same
(c) Force of attraction between the nucleus and valence electrons increases
(d) All of these
Answer : D

Assertion Reason type Questions

In the following questions a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
(A) Both assertion and reason are true and the reason is the correct explanation of assertion.
(B) Both assertion and reason are true and the reason is not the correct explanation of assertion.
(C) Assertion is true but the reason is false.
(D) Both assertion and reason are false.
(E) Assertion is false but reason is true.

Question. Assertion: Properties of an atom and its corresponding ion remains the same.
Reason: Electronic configurations of both atom and ion remain same.
Answer : D

Question. Assertion: Elements in the same vertical column have similar properties.
Reason: The properties of elements are periodic functions of their atomic numbers.
Answer : B

Question. Assertion: Fluorine is more reactive than Chlorine.
Reason: The chemical reactivity of non-metals increases down the group.
Answer : C

Question. Assertion: Group 18 elements are inert.
Reason: They have completely filled valence shell.
Answer : A

Question. Assertion: Isotopes of an element were given separate places in Mendeleev’s periodic table.
Reason: Isotopes of an element have different atomic masses.
Answer : E

Question. Assertion : In Mendeléev Periodic Table, cobalt was placed before nickel.
Reason : The atomic mass of cobalt is less than nickel
Answer : C

Question. Assertion : According to Mendeleev, periodic properties of elements is a function of their atomic number.
Reason : Atomic number is equal to the sum of number of protons and neutrons.
Answer : D

Question. Assertion: Li,Na,K belong to Dobereiner’s triads
Reason: The atomic mass of Na is the average of atomic masses of Li and K
Answer : A

Question. Assertion : Atomic size decreases along a period.
Reason : Effective nuclear charge decreases as the atomic number increases resulting in the increased attraction of electrons to the nucleus
Answer : C

Question. Assertion: Mendeleev left some gaps in his Periodic Table
Reason: Mendeleev believed that some elements would be discovered later
Answer : A

Question : Out of lithium and potassium, which one has stronger metallic character and why?
Answer : On going down in a group of the periodic table, the metallic character of elements increases. Therefore, potassium has stronger metallic character than Lithium. The reason behind is that as we go down in a group of the periodic table, one more electron shell is added. As a result, the size of the atom increases. The valence electrons move away from the nucleus at regular intervals. The holding capacity of the nucleus on valence electrons decreases. Due to this the atom can lose valence electrons more easily to form positive ions, and hence the metallic character increases. 

Question : An element X has mass number 35 and the number of neutrons is 18. Identify the group number and period of X. 
Answer : Mass no. = Sum of protons + Sum of neutrons
35 = Sum of protons + 18
Sum of protons = 35 – 18
Sum of protons = 17
Hence, we can say that the atomic number of element X is 17.
Its electronic configuration will be 2, 8, 7.
Thus it is clear that element X belongs to the 3rd Period and the 17^th Group

Question : List two anomalies of Mendeleev’s periodic table which were solved by modern periodic table law.
Answer : (i) Position of isotopes were not justified in Mendeleev’s periodic table but it is justified in the modern periodic table.
(ii) Increasing order of atomic masses could not be followed but increasing order of atomic numbers has been followed.

Question : Predict the maximum number of valence electrons possible for the elements in the first period of periodic table.
Answer : 2 valence electrons are present in the last element ‘Helium’ of 1st period.

Question : (a) Among the following elements identify the one that would form anions:
K, O, Na, F, Ca, Cl, Hg
(b) Write the electronic configuration of the anions identified above.
Answer : (a) O, F, Cl will form anions.
(b) O2–(10)         2, 8
       F–(10)          2, 8
      Cl–(18)          2, 8, 8.

Question : (a) State modern periodic law.
(b) Elements A, B, C and D have atomic numbers 1, 8, 11 and 19 respectively. Choose the odd element and give reason for your answer.
Answer : (a) Modern Periodic Law: It states that the properties of elements are a periodic function of their atomic number.
(b) ‘B’ with atomic number 8 is an odd element because it has 6 valence electrons whereas others have 1 valence electron.

Question : An element belongs to third period and second group of the periodic table:
(a) State number of valence electrons in it. (b) Is it a metal or non-metal?
(c) Name the element. (d) Write the formula of its oxide.
Answer : (a) 2, 8, 2 is the electronic configuration. The number of valence electrons = 2
(b) It is a metal
(c) Magnesium
(d) MgO is the formula of its oxide.

Question : Why lithium with atomic number 3 and potassium with atomic number 19 are placed in group one?
What will be atomic numbers of first two elements of second group?
Answer :  K L M N
Li(3)          2, 1
K(19)        2, 8, 8, 1
Li and K are placed in Group 1 because both have 1 valence electron.
Be(4) and Mg(12) are first two elements of Group 2.

Question : State the reasons for the following:
(a) The elements of the same group have similar chemical properties.
(b) The elements of the same period have different properties.
Answer : (a) It is because they have the same number of valence electrons.
(b) It is because they differ in the number of valence electrons.

Question : How it can be proved that the basic structure of the Modern Periodic Table is based on the electronic configuration of atoms of different elements?
Answer : Position of element in periodic table is decided with the help of electronic configuration e.g. group number is decided on the basis of valence electrons e.g., elements having valence electrons 1,2,3,4,5,6,7,8, belong to Group 1, 2, 13, 14, 15, 16, 17 and 18 respectively. Period is equal to number of shells e.g. 2,8,3 belong to third period.

Question : Choose from the following: ₆C, ₈O, ₁₀Ne, ₁₁Na, ₁₄Si
(a) Elements that should be placed in the same period.
(b) Elements that should be placed in the same group.
State the reason for your selection in each case. 
Answer : (a) ₆C, ₈O, ₁₀Ne belong to the same period because all these have 2 shells. ₁₁Na, ₁₄Si belong to the same period because both of these have 3 shells.
(b) ₆C and ₁₄Si belong to the same group because they have the same number of valence electrons and valency.

Question : The electronic configuration of an element is 2,8,4. State its:
(a) Group and period in the Modern Periodic Table.
(b) Name and write its one physical property.
Answer : (a) It belongs to Group 14, third period.
(b) Silicon is the element. It is a metalloid, forms covalent bond. It is a semiconductor.

Question : An element ‘X’ has atomic number 13.
(a) Write its electronic configuration.
(b) State the group to which ‘X’ belong.
(c) Is ‘X’ a metal or non-metal?
(d) Write the formula of its bromide.
Answer : (a) 2, 8, 3, (b) Group 13, (c) Metal, (d) AlBr₃

Question : (a) Predict the following which will form anions and which will form cations:
(i) Na (ii) Al (iii) Cl (iv) O
(b) Name two elements that are inert.
Answer : (a) Cl and O will form anions
Na and Al will form cations
(b) He, Ne are inert

Question : (a) State two main characteristics of elements on which modern periodic table is based.
(b) No fixed position can be assigned to hydrogen in the periodic table. Why?
Answer : (a) (i) Atomic number, (ii) No. of valence electrons
(b) It is because hydrogen resembles with Group 1 as well as Group 17 elements, therefore no fixed position can be assigned to it.

Question : The electrons in the atoms of four elements A, B, C and D are distributed in three shells having 1, 3, 5 and 7 electrons in the outermost shell respectively. State the period in which these elements can be placed in the modern periodic table. Write the electronic configuration of the atoms A and D and the molecular formula of compound formed when A and D will combine.
Answer : They belong to third period because these have 3 shells.
A has electronic configuration 2, 8, 1, valence electron 1, valency = 1
D has electronic configuration 2, 8, 7, valence electron 7, valency = 1
Formula: AD or A⁺D^–

Question : Name the element which has
(a) the electronic configuration 2, 8, 1
(b) a total of two shells, with 4 electrons in the valence shell.
(c) total of three shells, with 3 electrons in valence shell.
(d) One shell which is completely filled with electrons.
(e) twice as many electrons in the second shell as in the first shell.
Answer : 1. (a) Sodium (2, 8, 1)
(b) Carbon (2, 4)
(c) Aluminium (2, 8, 3)
(d) Helium (2)
(e) Carbon (2, 4)

Long Answers