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. $L{i}^{+},B{e}^{2+}$
• D. $B{a}^{2+},S{r}^{2+}$

Answer 1

Answer: (B)

$O^{2-},N^{3-}$

Consider the radius of the given species:-
A) $Na$ is larger than $Mg$ as size decreases as we move across a period from left to right.
B) $O^{2-}<N^{3-}$; Greater the electrons, more the repulsion and hence larger size.
C) $L{i}^{+}>B{e}^{2+}$; Greater effective nuclear charge.
D) $B{a}^{2+}>S{r}^{2+}$; Size increases as we move down a period.
Hence, option B is the right answer.