Question

Assertion: First ionisation energy for nitrosen is lower than oxygen.

Reason : Across a period effective nuclear charge decreases.

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

(b) Both A and R are true but R is not correct explanation of A  

(c) A is true but R is false  

(d) A and R are false

Answer 1

Correct option  (d) A and R are false

Explanation:

First ionisation energy for nitrogen is greater than oxygen.

This is due to stable configuration of nitrogen (halffilled 2p-orbital).

Due to screening effect, the valence electrons experience less attraction towards the nucleus. Due to this. the valence shell electrons do not feel the full charge of the nucleus. The actual nuclear charge felt by the valence shell electrons is termed effective nuclear charge and its magnitude increases in a period when we move from left to right.