The reaction $\left[\mathrm{Co}(\mathrm{CN})_{5} \mathrm{H}_{2} \mathrm{O}\right]^{2-}+\mathrm{X}^{-} \rightarrow\left[\mathrm{Co}(\mathrm{CN})_{5} \mathrm{X}\right]^{2-}+\mathrm{H}_{2} \mathrm{O}$ follows a/an
(a)Interchange dissociative ($I_d$) mechanism
(b)Dissociative (D) mechanism
(c)Associative (A) mechanism
(d)Interchange Associative ($I_a$) mechanism
Answer
Answer: B ✓ checked by 4AB · confidence medium
The source book printed A; on checking, B is correct — see the explanation.
Explanation
Anation of [Co(CN)₅(H₂O)]²⁻ is the classic limiting dissociative (D) case. The rate saturates in [X⁻], and the five-coordinate [Co(CN)₅]³⁻ intermediate is captured competitively (b).