Consider the following statements for the self-exchange electron transfer reaction in $\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+/3+}$
\[ \begin{array}{l} \text{A. } \sigma^{*} \text{ orbitals are only involved in electron transfer} \\ \text{B. It involves large inner-sphere reorganization energy} \\ \text{C. It involves no change in M--L bond lengths} \\ \text{D. Rate of self-exchange electron transfer is fast} \end{array} \]
The correct statements are
(a)A, B and D
(b)A and B
(c)A and C
(d)B and D
Answer
Answer: B ✓ checked by 4AB · confidence high
Explanation
Cr²⁺/Cr³⁺ self-exchange moves an e_g (σ*) electron. That changes the Cr–O bond lengths a lot (Jahn–Teller d⁴ vs d³), so the reorganisation energy is large and the exchange is slow. A and B (b).