The number of expected electronic transitions in $\left[\mathrm{Cr}(\mathrm{en})_{3}\right]^{3+}$ and $\operatorname{trans}-\left[\mathrm{Cr}(\mathrm{en})_{2} \mathrm{F}\right]^{+}$ at 4 K is, respectively (en = ethylenediamine)
(a)3 and 3
(b)3 and 4
(c)3 and 5
(d)3 and 6
Answer
Answer: D ✓ checked by 4AB · confidence high
Explanation
d³ in O_h: three spin-allowed bands (⁴A₂g → ⁴T₂g, ⁴T₁g(F), ⁴T₁g(P)). In the tetragonal trans complex each ⁴T term splits into two (E + A₂/B₂), so six bands are expected at 4 K.