Q28 · CSIR-NET Chemistry, December 2018
Paper: CSIR-NET December 2018 · Subject: Inorganic Chemistry · Chapter: Chemical Bonding · Topic: Chemical Bonding – General · Marks: 2 · Difficulty: Easy
The characters of LUMO and $\mathrm{CN}^{-}$and $\mathrm{O}_{2}$ respectively, are
(a)$\sigma_{\mathrm{g}}$ and $\pi_{\mathrm{u}}$
(b)$\pi$ and $\sigma_{u}$
(c)$\pi_{\mathrm{g}}$ and $\sigma_{\mathrm{u}}$
(d)$\sigma_{\mathrm{u}}$ and $\pi_{\mathrm{g}}$
Answer
Answer: B ✓ checked by 4AB · confidence high
The source book printed C; on checking, B is correct — see the explanation.
Printed C; a heteronuclear orbital cannot carry a g label.
Explanation
CN⁻ is heteronuclear, so its π* LUMO has no g/u label; O₂'s LUMO is σ*_u(2p). Hence '— and u'.
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