Question

Which among the following sets of atomic numbers is/are associated with the increasing order of the number of unpaired electrons?

(a) Z = 29; Z = 20; Z = 25; Z = 27; Z = 24

(b) Z = 20; Z = 29; Z = 22; Z = 27; Z = 25

(c) Z = 19; Z = 22; Z = 24; Z = 26; Z = 25

(d) Z = 19; Z = 22; Z = 26; Z = 25; Z = 24

• A. a and c
• B. b and d
• C. a and d
• D. b and c

Answer 1

The correct option is B b and d

The electronic configuration of various atomic number's can be written as;

Atomic no. 19; $\left[Ne\right]3s^{2}3p^{6}4s^1$; no. of unpaired electron = 1

Atomic no. 20; $\left[Ne\right]3s^{2}3p^{6}4s^2$; no. of unpaired electron = 0

Atomic no. 22; $\left[Ne\right]3s^{2}3p^{6}4s^{2}3d^2$; no. of unpaired electron = 2

Atomic no. 24; $\left[Ne\right]3s^{2}3p^{6}4s^{1}3d^5$; no. of unpaired electron = 6

Atomic no. 25; $\left[Ne\right]3s^{2}3p^{6}4s^{2}3d^5$; no. of unpaired electron = 5

Atomic no. 26; $\left[Ne\right]3s^{2}3p^{6}4s^{2}3d^6$; no. of unpaired electron = 4

Atomic no. 27; $\left[Ne\right]3s^{2}3p^{6}4s^{2}3d^7$; no. of unpaired electron = 3

Atomic no. 29; $\left[Ne\right]3s^{2}3p^{6}4s^{1}3d^{10}$;no. of unpaired electron = 1

Increasing order of no. of lone pairs, atomic no. wise is:

$20<19=29<22<27<26<25<24$

(b) and (d) shows the correct order.

Therefore option (B) is correct.