This set of Class 11 Chemistry Chapter 2 Multiple Choice Questions & Answers (MCQs) focuses on “Quantum Mechanical Model of Atom”.

1. The principal quantum number describes ____

a) energy and size of the orbit

b) the shape of the orbital

c) spatial orientation of the orbital

d) the spin of the electron

View Answer

Explanation: Among the four quantum numbers, the principal quantum number describes the size and energy of the orbit. It is represented by the symbol “n”. For shells, K, L, M, N and O, n is given by 1, 2, 3, 4 and 5.

2. What is the shape the orbital, whose “l” is 1?

a) Spherical

b) Dumbbell

c) Double dumbbell

d) Complex

View Answer

Explanation: The azimuthal quantum number is given by “l”. When l = 0, 1, 2 and 3, they are s-orbital, p-orbital, d-orbital and f-orbital respectively. The shapes of s-orbital, p-orbital, d-orbital, and f-orbital are Spherical, Dumbbell, Double dumbbell and Complex respectively.

3. What is the magnetic quantum number of the orbital 2p_{z}?

a) 1

b) ±1

c) -1

d) 0

View Answer

Explanation: The magnetic quantum of an orbital range from -( l – 1) to l – 1. Its symbol is given by m. For 2p orbital, there are 3 magnetic quantum numbers namely -1, 0 and 1. For 2p

_{z}orbital its 0, taken that z is the internuclear axis.

4. Total number of nodes for 3d orbital is ________

a) 3

b) 2

c) 1

d) 0

View Answer

Explanation: Total number of nodes include angular and radial nodes. Angular nodes and radial nodes are given by the formula n – l -1 and l respectively. So the total number of nodes are n – l -1 + l = n – 1. For 3d orbit, “n” is 3, so total number nodes is 3 – 1 = 2.

5. Which of the following set of quantum numbers is not valid?

a) n = 5, l = 2, m = 0, s = 1/2

b) n = 1, l = 2, m = 0, s = 1/2

c) n = 5, l = 3, m = 2, s = 1/2

d) n = 5, l = 2, m = 0, s = -1/2

View Answer

Explanation: The set of quantum number n = 1, l = 2, m = 0, s = 1/2, is not valid because the value of azimuthal quantum number should lie only in between 0 and n-1, where n is principal quantum number. So the above set of quantum numbers is not valid.

6. According to the Aufbau’s principle, which of the following orbital should be filled first?

a) 5d

b) 4p

c) 3p

d) 2s

View Answer

Explanation: As per the Aufbau’s principle, the orbital or subshell with the lowest energy should be filled first. The ascending order of orbital’s energy is given by 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 4f, 5d, 6p, 7s. So 2s orbital should be filled first.

7. No two electrons have the same set of all four quantum numbers.

a) True

b) False

View Answer

Explanation: Yes, no two electrons have the same set of all four quantum numbers. This is explained by Pauli’s exclusive principle. At most electrons can have all 3 quantum numbers the same as they are in the same orbital. But the spin quantum number’s values are different.

8. The below process of filling electrons in an orbital follows __________

a) Aufbau principle

b) Hund’s rule of maximum multiplicity

c) Pauli’s exclusive principle

d) Electronic configuration

View Answer

Explanation: According to Hund’s rule of maximum multiplicity, the pairing of electrons cannot be started until each of the orbitals is singly occupied. The reason behind this is that the half-filled or fully filled orbitals are much more stable comparatively.

9. How many electrons can exist with the principal quantum number’s value as 4?

a) 16

b) 4

c) 32

d) 12

View Answer

Explanation: The number of orbitals within an orbit is n2. But as each orbital can accommodate 2 electrons, the number of electrons that can exist with the “n” as the principal quantum number is 2n

^{2}. So here 2n

^{2}= 2(4)

^{2}= 2(16) = 32.

10. Write the values for l, n, and m for Ψ_{3,1,0}?

a) 1, 3, 0

b) 3, 1, 0

c) 0, 3, 1

d) 1, 0, 3

View Answer

Explanation: The representation of the Schrodinger wave function is given by Ψ

_{n,l,m}. Therefore by comparing Ψ

_{n,l,m}and Ψ

_{3,1,0}we get that n = 3, l = 1 and m = 0. Here n, l, and m are principal, azimuthal and magnetic quantum numbers respectively.

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