Q. 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) ${Ba}^{2 +},\ Sr^{2 +}$
Explanation
(b)
$O^{- 2}and\ N^{3 -}$ both are isoelectronic but differ in the charge possessed by them. As the negative charge increase, the electrons are held less and less tightly by the nucleus, therefore ionic radii increases. Hence, ionic radii of $N^{3 -}$ is greater than $O^{2 -}$.
In a period from left to right atomic radii decreases but in a group on moving downwards it increases.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.