Question

Assertion (A): The first ionization enthalpy of nitrogen is higher than that of oxygen.
Reason (R): Nitrogen has a half-filled \(2p\) orbital, which is extra stable.

• A. A and R are both true, and R is the correct explanation of A.
• B. A and R are both true, but R is not the correct explanation of A.
• C. A is true, but R is false.
• D. A is false, but R is true.

Hint:

Remember the important exception in ionization enthalpy: \[ \boxed{IE_1(N)\gt IE_1(O)} \] because \[ \boxed{N:2p^3} \] is a stable half-filled configuration, whereas oxygen has one paired electron in the \(2p\) subshell, making electron removal easier.

Answer 1

The Correct Option is A

Nitrogen ($2p^3$) possesses a stable half-filled $p$ subshell, which requires extra energy to remove an electron. Oxygen ($2p^4$) has one paired $p$ orbital whose electron-electron repulsion makes it easier to ionise, so $IE_1(N) > IE_1(O)$ and the reason correctly explains the assertion.