## Atomic Structure Questions and Answers Part-2

1. Which of the following statements in relation to the hydrogen atom is correct?
a) 3s orbital is lower in energy than 3p orbital
b) 3p orbital is lower in energy than 3d orbital
c) 3s and 3p orbitals are of lower energy than 3d orbital
d) 3s, 3p and 3d orbitals all have the same energy

Explanation: A hydrogen atom has 1st configuration and these its 3p and 3d orbitals will have same energy with respect to 1s orbital.

2. Which one of the following sets of ions represents a collection of isoelectronic species? (Atomic nos.: F = 9, Cl = 17, Na = 11, Mg = 12, Al = 13, K = 19, Ca = 20, Sc = 21)
a) K+, Ca2+, Sc3+, Cl
b) Na+, Ca2+, Sc3+, F
c) K+, Cl, Mg2+, Sc3+
d) Na+, Mg2+, Al3+, Cl

Explanation: Isoelectronic species are those which have same number of electrons. K+ = 19 – 1 = 18; Ca2+ = 20 – 2 = 18; Sc3+ = 21 – 3 = 18; Cl = 17 + 1 = 18. Thus all these ions have 18 electrons in them.

3. Which of the following statements in relation to the hydrogen atom is correct?
a) 3s orbital is lower in energy than 3p orbital
b) 3p orbital is lower in energy than 3d orbital
c) 3s and 3p orbitals are of lower energy than 3d orbital
d) 3s, 3p and 3d orbitals all have the same energy

Explanation: Auf-bau principle is not applicable for H atom.

4. Consider the ground state of Cr atom (Z = 24). The numbers of electrons with the azimuthal quantum numbers, l = 1 and 2 are, respectively:
a) 12 and 4
b) 12 and 5
c) 16 and 4
d) 16 and 5

Explanation: 24Cr → 1s2 2s22p6 3s2 3p6 3d5 4s1
As we know for p, l = 1 and d, l = 2
For l = 1, total number of electrons = 12 [2p6 and 3p6]
For l = 2, total number of electrons = 5 [3d5]

5. A body of mass 10 mg is moving with a velocity of 100 ms-1. The wavelength of de-Broglie wave associated with it would be (Note: h = 6.63 × 10-34 Js)
a) 6.63 × 10-37 m
b) 6.63 × 10-31 m
c) 6.63 × 10-34 m
d) 6.63 × 10-35 m

Explanation: m = 10 mg
= 10 × 10-6 kg
v = 100 ms-1
λ = (h)/(mv)
= (6.63×10-34)/ (10 × 10-6 × 100)
= 6.63 × 10-31 m

6. Which of the following statements does not form a part of Bohrs model of hydrogen atom?
a) Energy of the electrons in the orbit is quantised
b) The electron in the orbit nearest the nucleus has the lowest energy
c) Electrons revolve in different orbits around the nucleus
d) The position and velocity of the electrons in the orbit cannot be determined simultaneously

Explanation: The position and velocity of electrons cannot be determined simultaneously does not fit in with the Bohrs model of H atom. It is a part of Heisenbergs uncertainty principle

7. A sub-shell with n = 6, l = 2 can accommodate a maximum of
a) 12 electrons
b) 36 electrons
c) 10 electrons
d) 72 electrons

Explanation: n = 6, ℓ = 2 means 6d → will have 5 orbitals. Therefore max 10 electrons can be accommodated as each orbital can have maximum of 2 electrons.

8. In the ground state, an element has 13 electrons in its M-shell. The element is_____.
a) Copper
b) Chromium
c) Nickel
d) Iron

Explanation: M shell means it is third shell ⇒ n = 3
Number of electrons in M shell = 13
⇒ 3s23p63d5
The electronic configuration is: (1s2) (2s2 2p6) (3s2 3p6 3d5) (4s1)
The element is chromium is Cr.

9. The magnetic quantum number specifies
a) Size of orbitals
b) Shape of orbitals
c) Orientation of orbitals
d) Nuclear Stability

Explanation: The magnetic quantum number specifies orientation of orbitals.

10. Which of the following element has least number of electrons in its M-shell?
a) K
b) Mn
c) Ni
d) Sc