Question

Peroxide ion............ (i) has five completely filled anti bonding 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. (i) and (iv)

Answer 1

Answer: (A)

Peroxide ion is $O_2^{2-}$ . $O_2^{2-}(18)=\sigma 1s^2,$ ${}_{\sigma }^{\ast }1s^2,$ $\sigma 2s^2,$ ${}_{\sigma }^{\ast }2s^2,$ $\sigma 2p_z^2,$ $\pi 2p_x^2\approx \pi 2p_y^2{,}_{\pi }^{\ast }2p_x^2{\approx }_{\pi }^{\ast }2p_y^2$ Bonds 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.