Out of H and `H_(2)` , the latter has higher first ionization energy while out of O and `O_(2)` , the former has higher first ionization energy . Explain why .

Explanation

In `H_(2)` , first electron has to be removed from `sigma` (1s) which has lower energy (more stable ) than H-atom . In
`O_(2)` first electron has to be removed from `pi^(**) (2p_(x)) or pi^(**) (2p_(y))` orbitals which has higher energy than 2 p -
orbital of O-atom .