Key Idea Ionisation energy usually increases from left to right in a period with decrease in atomic size and decreases from upto down in a group with increase in atomic size.
$\begin{array}{lc}\text { Electronic configuration } & \text { Group } \\ {[\mathrm{Ne}] 3 \mathrm{~s}^2 3 \mathrm{p}^3} & \mathrm{~V} \\ {[\mathrm{Ne}] 3 \mathrm{~s}^2 3 \mathrm{p}^2} & \text { IV } \\ {[\mathrm{Ar}] 3 \mathrm{~d}^{10}, 4 \mathrm{~s}^2, 4 \mathrm{p}^3} & \mathrm{~V} \\ {[\mathrm{Ne}] 3 \mathrm{~s}^2 3 \mathrm{p}^1} & \text { III }\end{array}$
Since IE increases in a period and decreases in a group, [Ne] $3 s^2 3 \mathrm{p}^3$ configuration has the highest ionisation energy among the given.