Paper: CSIR-NET December 2019 · Subject: Inorganic Chemistry · Chapter: Chemical Bonding · Topic: Chemical Bonding – General · Marks: 2 · Difficulty: Hard
Choose the correct order of energy of $2 \sigma_{\mathrm{g}}$ and $1 \pi_{0}$ molecular orbitals for $\mathrm{B}_{2}, \mathrm{C}_{2}$ and $\mathrm{O}_{2}$ :
(a)$2 \sigma_{\mathrm{g}}>1 \pi_{\mathrm{u}}$ for all the three
(b)$2 \sigma_{\mathrm{g}}>1 \pi_{\mathrm{u}}$ for $\mathrm{B}_{2}$ and $\mathrm{C}_{2}$ only
(c)$1 \pi_{\mathrm{u}}>2 \sigma_{\mathrm{g}}$ for $\mathrm{C}_{2}$ and $\mathrm{O}_{2}$ only
(d)$2 \sigma_{g}>1 \pi_{u}$ for $\mathrm{B}_{2}$ and $\mathrm{O}_{2}$ only
Answer
Answer: B ✓ checked by 4AB · confidence high
Explanation
For B₂ and C₂ strong s–p mixing pushes 2σ_g above 1π_u; for O₂ (and F₂) the mixing is weak and 2σ_g lies below 1π_u.