Question

Given below are two statements. One is labelled as Assertion A and the other is labelled as Reason R.
$\text{Assertion A:}$The first ionization enthalpy for oxygen is lower than that of nitrogen.
$\text{Reason R:}$ The four electrons in 2p orbitals of oxygen experience more electron-electron repulsion.
In the light of the above statements, choose the correct answer from the options given below.

• A. Both A and R are correct but R is NOT the correct explanation of A
• B. A is not correct but R is correct
• C. A is correct but R is not correct
• D. Both A and R are correct and R is the correct explanation of A

Answer 1

The correct option is D Both A and R are correct and R is the correct explanation of A

Ionisation energy = N > O. In oxygen atom, 2 of the 4 2p electrons must occupy the same 2p orbital resulting in an increased electron electron-repulsion.
Nitrogen has half filled p-orbital which is stable. Due to this it’s 1st ionization energy is more than oxygen.