Assertion: N2 is less reactive than P4.

Reason: Nitrogen has more electron gain enthalpy than phosphorus.

1. Both Assertion and Reason are correct statements, and Reason is the correct explanation of the Assertion.

2. Both Assertion and Reason are correct statements, and Reason is not the correct explanation of the Assertion.

3. Assertion is correct, but Reason is the wrong statement.

4. Assertion is wrong but Reason is the correct statement.

Hint: N2 has a triple bond and P4 has a single bond
 
N2 is less reactive than P4 due to the high value of bond dissociation energy which is due to the presence of a triple bond
 
between two N-atoms of Nmolecule. But in P4 only a single bond is present. 
 
Hence, Assertion is correct, but Reason is the wrong statement.