A true statement about base hydrolysis of $\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{Cl}\right]^{2+}$ is:
(a)It is a first order reaction
(b)The rate determining step involves the dissociation of chloride in $\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4}\left(\mathrm{NH}_{2}\right) \mathrm{Cl}\right]^{+}$
(c)The rate is independent of the concentration of the base.
(d)The rate determining step involves the abstraction of a proton from $\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{Cl}\right]^{2+}$
Answer
Answer: B ✓ checked by 4AB · confidence high
Explanation
S_N1CB: fast pre-equilibrium deprotonation of NH₃, then rate-determining loss of Cl⁻ from the amido conjugate base [Co(NH₃)₄(NH₂)Cl]⁺; the rate is second order (first in complex and in OH⁻).