Options :

1. I.E.₁ of O is lower than that of N but I.E.₂ O is higher than that of N

2. The enthalpy of N to gain an electron is almost zero but of P is 74.3 kJ mol⁻¹

3. The covalent radius of iodine is less than its Van der Waal’s radius

4. isoelectronic ions belong to the same period