Question

In which one of the following pairs the radius of the second species is greater than that of the first?

(a) ${Na}, {Mg}$

(b) ${O}^{2-}, {N}^{3-}$

(c) ${Li}^{+}, {Be}^{2+}$

(d) ${Ba}^{2+}, {Sr}^{2+}$

Answer 1

Correct Option: (B)

Explanation —

${N}^{3-}$ and ${O}^{2-}$ both are isoelectronic but differ in the charge possessed by them. As the nuclear charge decreases from ${O}$ to ${N}$, the electrons are held less and less tightly by the nucleus. Hence, the ionic size increases from ${O}^{2-}$ to ${N}^{3-}$.