JEE Main · 2026 · 22 Jan 2026 · Shift 1 · Coordination Compounds

Consider the transition metal ions

Mn^{3 +}, Cr^{3 +}, Fe^{3 +}

and

Co^{3 +}

and all form low spin octahedral complexes. The correct decreasing order of unpaired electrons in their respective d-orbitals of the complexes is

Answer: (D)

Solution

In a strong (low-spin) octahedral field the five d orbitals split into a lower

t_{2 g}

set and an upper

e_{g}

set, and electrons fill and pair within

t_{2 g}

before entering

e_{g}

. For

C r^{3 +}

(

d^{3}

t_{2 g}^{3}

leaves 3 unpaired electrons; for

M n^{3 +}

(

d^{4}

t_{2 g}^{4}

leaves 2; for

F e^{3 +}

(

d^{5}

t_{2 g}^{5}

leaves 1; and for

C o^{3 +}

(

d^{6}

t_{2 g}^{6}

leaves 0. The decreasing order of unpaired electrons is

C r^{3 +} > M n^{3 +} > F e^{3 +} > C o^{3 +}

JEE Main · 2026 · 22 Jan 2026 · Shift 1 · Single correct option