Question

The correct order of $Ist$ ionization potential among following elements $Be,B,C,N,O$ is

• A. $B<Be<C<O<N$
• B. $B<Be<C<N<O$
• C. $Be<B<C<N<O$
• D. $Be<B<C<O<N$

Answer 1

The correct option is A $B<Be<C<O<N$

Because of extra stability of exactly half-filled electronic configuration of $N$ its $I{E}_1$ is higher than that of $O$. Further because of higher nuclear charge , $I{E}_1$ of $C$ is higher than that of $Be$ and $B$.
Among $Be$ and $B$ , the $I{E}_1$ of $Be$ is higher than that of $B$ because in case of $Be$ a $2s$- electron is to removed while in case of $B$ a $2p$-electron is to be removed. Thus, the overall order is (a) i.e., $B<Be<C<O<N$.