The correct statement about the substitution reaction of $\left[\mathrm{Co}(\mathrm{CN})_{5}\mathrm{Cl}\right]^{3-}$ with $\mathrm{OH}^{-}$ to give $\left[\mathrm{Co}(\mathrm{CN})_{5}(\mathrm{OH})\right]^{3-}$ is,
(a)it obeys first order kinetics
(b)its rate is proportional to the concentration of both the reactants
(c)it follows the $\mathrm{S_{N}}1_{\mathrm{CB}}$ mechanism
(d)its rate is dependent only on the concentration of $[\mathrm{OH}]^{-}$
Answer
Answer: A ✓ checked by 4AB · confidence high
Explanation
[Co(CN)₅Cl]³⁻ has no N–H protons, so S_N1CB is impossible; it substitutes by a dissociative (D) path whose rate depends only on the complex — first-order, independent of [OH⁻].