JEE Main 2026 — Jan 23, Shift 1 — Chemistry solution

JEE Main2026Jan 23, Shift 1Chemistry

The crystal field splitting energy of [Co(oxalate) $_{3}$ ] $^{3 -}$ complex is 'n' times that of the [Cr(oxalate) $_{3}$ ] $^{3 -}$ complex. Here 'n' is ______. [Assume $Δ_{0} ≫ P$ ]

Your answer

Solution

With $Δ_{0} ≫ P$ , pairing energy is neglected and both complexes are treated as low-spin (or in Cr's case, the usual $d^{3}$ configuration).

[Co(ox) $_{3}$ ] $^{3 -}$ : Co $^{3 +}$ , $d^{6}$ , low-spin → $t_{2 g}^{6} e_{g}^{0}$ .

CFSE $= 6 \times (- 0.4 Δ_{0}) = - 2.4 Δ_{0}$ .

[Cr(ox) $_{3}$ ] $^{3 -}$ : Cr $^{3 +}$ , $d^{3}$ → $t_{2 g}^{3} e_{g}^{0}$ .

CFSE $= 3 \times (- 0.4 Δ_{0}) = - 1.2 Δ_{0}$ .

Ratio: $\frac{( CFSE ) _{Co}}{( CFSE ) _{Cr}} = \frac{- 2.4 Δ _{0}}{- 1.2 Δ _{0}} = 2$ .

$∴ n = 2$ .

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