Q22 / 75 · JEE Main 2026 (28 January Shift 2) · Chemistry
The number of isoelectronic species among $\mathrm{Sc}^{3+}, \mathrm{Cr}^{2+}, \mathrm{Mn}^{3+}, \mathrm{Co}^{3+}$ and $\mathrm{Fe}^{3+}$ is ' $\mathrm{n}^{\prime}$. If ' $\mathrm{n}^{\prime}$ moles of AgCl is formed during the reaction of complex with formula $\mathrm{CoCl}_{3}(\mathrm{en})_{2} \mathrm{NH}_{3}$ with excess of $\mathrm{AgNO}_{3}$ solution, then the number of electrons present in the $t_{2 g}$ orbital of the complex is $\_\_\_\_$.
Correct answer: 6
Solution
For the complex CoCl₃(en)₂NH₃, cobalt is in +3 oxidation state with electron configuration [Ar]3d⁶.
In an octahedral field with strong field ligands (ethylenediamine, ammonia, chloride), Co³⁺ forms a low-spin complex with $t_{2g}^6 e_g^0$ configuration.
The $t_{2g}$ orbitals consist of $d_{xy}$, $d_{xz}$, and $d_{yz}$.
With all 6 electrons filling the three $t_{2g}$ orbitals, the total number of electrons in the $t_{2g}$ orbital set is 6.
In an octahedral field with strong field ligands (ethylenediamine, ammonia, chloride), Co³⁺ forms a low-spin complex with $t_{2g}^6 e_g^0$ configuration.
The $t_{2g}$ orbitals consist of $d_{xy}$, $d_{xz}$, and $d_{yz}$.
With all 6 electrons filling the three $t_{2g}$ orbitals, the total number of electrons in the $t_{2g}$ orbital set is 6.
Hence, the correct answer is 6.