Question

(c) The Ist ionisation energy of nitrogen is greater than that of oxygen
while the reverse is true for second ionisation energy​

Answer 1

The electronic configuration of oxygen is 1s2, 2s2, 2p4 and the electronic configuration of nitrogen is 1s2, 2s2, 2p3.

The half or fully filled electronic configuration are considered a way more stable than others.

Since, Nitrogen possess half filled p orbital hence, being more stable and requiring a greater first ionisation energy than oxygen.

Now, when first loosely packed electron will be removed from oxygen and nitrogen then their electronic configurations will become::

Of Oxygen: 1s2, 2s2, 2p3

and, Of Nitrogen: 1s2, 2s2, 2p2

Now, as we can see electronic configuration of oxygen has half filled p orbital hence making oxygen way more stable than nitrogen thus, requiring greater second ionisation energy than nitrogen.