d
Ionisation energy usually increases from left to right in a period with a decrease in atomic size and decrease from up to down in a group with an increase in atomic size.

\(\left[\text {Ne}\right] 3 s^{2} 3 p^{3}=\text { Group } V\)

\([\mathrm{Ne}] 3 \mathrm{s}^{2} 3 \mathrm{p}^{2}=\) \(\mathrm{IV}\)

\([\mathrm{Ar}] 3 \mathrm{d}^{10} 4 \mathrm{s}^{2} 4 \mathrm{p}^{3}=\) Group \(\mathrm{V}\)

\(\left[\text {Ne}\right] 3 s^{2} 3 p 1=\) Group \(\mathrm{III}\)