Which of the following species has lowest ionisation potential?

Options

A. O
B. `O_(2)`
C. `O_(2)^(+)`
D. `O_(2)^(-)`

Answer

D

Explanation

In O-atom , the electron is to be removed from 2p
while in `O_(2) , O_(2)^(+) and O_(2)^(-)` , electron is to be
removed from `pi^(**) (2p_(x)) or pi^(**) (2p_(y))` which has
higher energy and hence less stable . Further , `O_(2)^(-)`
is least stable due to greater number of electrons
in the antibonding molecular orbitals .