Question

Assertion (A): The first ionization enthalpy for oxygen is lower than that of nitrogen.

Reason (R): The four electrons in 2p orbitals of oxygen experience more electron-electron repulsion.
In light of the above statements, choose the correct answer from the options given below.

Options

• Both (A) and (R) are correct and (R) is the correct explanation of (A). 

• Both (A) and (R) are correct and (R) is NOT the correct explanation of (A).

• (A) is correct but (R) is not correct.

• (A) is not correct but (R) is correct.

Answer 1

Both (A) and (R) are correct and (R) is the correct explanation of (A).

Explanation:

Oxygen's electronic configuration is partially filled compared to nitrogen's half-filled stability, oxygen has a lower ionisation energy than nitrogen. It is easier to remove the electron from partially filled oxygen atom as in doing so it attains half-filled stability. In the instance of nitrogen, it took more energy to remove an electron from an orbital that was partially or completely filled.

Electronic configuration of O = 1s² 2s² 2p⁶

Electronic configuration of N = 1s² 2s² 2p³ 

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.