Among the complexes, (A) $\mathrm{K}_{4}\left[\mathrm{Cr}(\mathrm{CN})_{6}\right]$, $\mathrm{K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]$, (C) $\mathrm{K}_{3}\left[\mathrm{Co}(\mathrm{CN})_{6}\right]$, (D) $\mathrm{K}_{4}\left[\mathrm{Mn}(\mathrm{CN})_{6}\right]$, and Jahn-Teller distortion is expected in
(a)A, B and C
(b)B, C and D
(c)A and D
(d)B and C
Answer
Answer: C ✓ checked by 4AB · confidence high
Explanation
Low-spin Cr(II) (t₂g⁴) and low-spin Mn(II) (t₂g⁵) have unevenly filled t₂g sets and distort; low-spin Fe(II) and Co(III) (t₂g⁶) do not. A and D.