The set containing the elements with positive electron gain enthalpies is

Assertion (A) : The ionic radii of $\mathrm{Na}^{+}$and $\mathrm{F}^{-}$are same.

Reason (R) : Both $\mathrm{Na}^{+}$and $\mathrm{F}^{-}$are isoelectronic species.

The correct answer is

In which of the following ionic pairs, second ion is smaller in size than the first ion?

In which of the following species, the ratio of $s$-electrons to $p$-electrons is same?