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During change of $O_2$ to $O_2^-$ ion, the electron adds on which one of the following orbitals?
A
$\sigma$ orbital
B
$\pi^*$ orbital
C
$\pi$ orbital
D
$\sigma^*$ orbital
Detailed Solution
$O_2$ (16 e⁻): $\sigma1s^2\,\sigma^*1s^2\,\sigma2s^2\,\sigma^*2s^2\,\sigma2p_z^2\,\pi2p_x^2 = \pi2p_y^2\,\pi^*2p_x^1 = \pi^*2p_y^1$
The $\pi^*2p$ orbitals are only half filled, so the extra electron of $O_2^-$ enters a $\pi^*$ orbital.
The $\pi^*2p$ orbitals are only half filled, so the extra electron of $O_2^-$ enters a $\pi^*$ orbital.