Assertion(A):  ${\mathrm{POF}}_3$ Exist but  ${\mathrm{NOF}}_3$ Does not exist
Reason (R): Phosphorus can form five bonds by expanding its octet while Nitrogen can not expand its octet to form five bonds

Assertion is true, Reason is true but Reason is correct explanation for Assertion

Assertion is true, Reason is false 

Assertion is false, Reason is true 

Assertion is true, Reason is true and Reason is not the correct explanation for Assertion