The correct order of second ionisation enthalpy (IE2) of Be, B, C and N is

$\mathrm{IE_2}$ removes an electron from the monovalent cation. $\mathrm{Be^+}$ ($2s^1$) loses an easily removed outer $s$ electron: lowest. $\mathrm{B^+}$ is $2s^2$ (stable, filled subshell), so $\mathrm{IE_2}$ is high; $\mathrm{C^+}$ is $2s^22p^1$ and loses the $2p$ electron more easily than $\mathrm{B^+}$ loses a $2s$ electron. $\mathrm{N^+}$ is $2s^22p^2$ with higher nuclear charge. Order (kJ/mol): Be $1757$ < C $2353$ < B $2427$ < N $2856$.