Explanation:
1. Statement (I): Incorrect. - The oxidation state of an element is not determined based on electron gain enthalpy. Instead, it is based on the number of electrons lost, gained, or shared during bond formation.
2. Statement (II): Correct. - \( p\pi-p\pi \) bond formation is more common in second-period elements (e.g., \( C, N, O \)) due to their small size and effective overlap of \( p \)-orbitals, which diminishes in larger elements from lower periods.
Final Answer is Option (4).