Question

Assertion : First ionisation energy for nitrogen is lower than oxygen.
Reason : Across a period effective nuclear charge decreases.

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (D)

In a group from left to right atomic number or nuclear charge or effective nuclear charge increase and size decrease, as a result ionisation energy increase. But elements of IIA and $VA$ group on the account of their half filled and completely filled orbitals respectively have stable configuration and so to remove electron from them comparatively larger energy has to be supplied.
$IA<IIA>IIIA<IVA<VA>VIA<VIIA$
The ionisation energy of $N(VA)$ is more than $O$ (VIA)