Question

Peroxide ion ______________
(i) has five completely filled antibonding molecular orbitals
(ii) is diamagnetic
(iii) has bond order one
(iv) is isoelectronic with neon

Which one of these is correct?

• A. (ii) and (iii)
• B. (i), (ii) and (iv)
• C. (i), (ii) and (iii)
• D. (ii) and (iv)

Answer 1

The correct option is A (ii) and (iii)

Peroxide ion is $O_2^{2-}$

$O_2^{2-}\left(18\right)=\sigma 1s^2,{\sigma }^{\ast }1s^2,\sigma 2s^2,{\sigma }^{\ast }2s^2,\sigma 2p_z^2,\pi 2p_x^2=\pi 2p_y^2,{\pi }^{\ast }2p_x^2={\pi }^{\ast }2p_y^2$

Bond order $=\frac{N_b-N_a}{2}=\frac{10-8}{2}=1$

It contains four completely filled antibonding molecular orbitals. Since all the electrons are paired, $O_2^{2-}$ is diamagnetic.

Peroxide ion is isoelectronic with argon, not with neon.