JEE Main 2026 — Coordination Compounds Question with Solution

In an octahedral complex, the d-orbitals split into $t_{2g}$ and $e_g$ levels.

For $d^3$: Configuration is $t_{2g}^3{e}_g^0$. Number of unpaired electrons = $3$.

For $d^4$ (low spin): Configuration is $t_{2g}^4{e}_g^0$. Number of unpaired electrons = $2$.

For $d^5$ (high spin): Configuration is $t_{2g}^3{e}_g^2$. Number of unpaired electrons = $5$.

For $d^6$ (high spin): Configuration is $t_{2g}^4{e}_g^2$. Number of unpaired electrons = $4$.

For $d^7$ (low spin): Configuration is $t_{2g}^6{e}_g^1$. Number of unpaired electrons = $1$.

Total number of unpaired electrons = $3+2+5+4+1=15$.

Answer: $15$