Question

The first ionisation energy of $Na,B,N$ and $O$ atoms follow the order:

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

Answer 1

The correct option is B $Na<B<O<N$

Ionisation energy increases along the period due to an increase in nuclear charge. However, ionisation energy for $N$ is more than $O$ due to half-filled subshell of $N$. Half-filled subshell imparts some extra stability to $N$, making it difficult to ionize.

Hence, the order will be: $Na<B<O<N$.