Question

Which one of the following elements has the highest first ionization potential?

• A. $C$
• B. $N$
• C. $B$
• D. $O$

Answer 1

The correct option is B $N$

Nitrogen has the highest first ionization energy, though it should have less than that of oxygen while going across a period. The electronic configuration of nitrogen is ${1s}^2,{2s}^2,{2p}_x^1,{2p}_y^1,{2p}_z^1$. Nitrogen has three electrons in $2p$ subshell which are singly filled. So, by Hund's Rule, half filled and fully filled orbitals are most stable. So, nitrogen is in a stable state and does not want to lose electrons. Hence, it has the highest first ionization energy.