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Q.
The ionisation energy of nitrogen is larger than that of oxygen because of
Uttarkhand PMTUttarkhand PMT 2010
Solution:
The ionisation energy of nitrogen is larger than that of oxygen because nitrogen has half-filled orbitals and thus, a more stable configuration.
$N(7)=1 s^{2}, 2 s^{2}, 2 p_{x}^{1}, 2 p_{y}^{2}, 2 p_{z}^{1}$
(half-filled, thus stable)
$O(8)=1 s^{2}, 2 s^{2}, 2 p_{x}^{2}, 2 p_{y}^{1}, 2 p_{z}^{1}$
(less stable)
Exactly half-filled and completely filled configuration have extra stability.