Class 12 NEET Chemistry Coordination Compounds

Concept: In an octahedral field, a low spin $d^6$ complex has all 6 electrons paired in the lower energy $t_{2g}$ orbitals.Explanation:In an octahedral crystal field, the d-orbitals split into a lower energy $t_{2g}$ set and a higher energy $e_g$ set. The energy of each electron in the $t_{2g}$ orbital is $-\frac{2}{5}\Delta_o$ (or $-0.4\Delta_o$).For a low spin $d^6$ complex, the electrons will pair up in the $t_{2g}$ orbitals before occupying the $e_g$ orbitals. Thus, the electronic configuration is $t_{2g}^6 e_g^0$.The total energy is calculated by multiplying the number of electrons in the $t_{2g}$ level by its energy and adding the pairing energy ($P$) for the electron pairs formed:$$\text{Energy} = 6 \times \left(-\frac{2}{5}\Delta_o\right) + 3P$$$$\text{Energy} = -\frac{12}{5}\Delta_o + 3P$$Here, $3P$ accounts for the 3 pairs of electrons in the $t_{2g}$ orbitals.Answer: Option B