Reaction of $\left[\mathrm{Ru}\left(\mathrm{NH}_{3}\right)_{5}(\text{isonicotinamide})\right]^{3+}$ with $\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}$ occurs by inner sphere mechanism and rate of the reaction is determined by dissociation of the successor complex. It is due
(a)Inert ruthenium birdged to inert chromium centre
(b)Inert ruthenium bridged to labile chromium centre
(c)Labile ruthenium bridged to inert chromium centre
(d)Labile ruthenium bridged to labile chromium centre
Answer
Answer: A ✓ checked by 4AB · confidence high
Explanation
Both the Ru(II/III) ammine and the Cr(III) aqua centres are substitution-inert, so the bridged successor complex breaks up slowly and its dissociation becomes rate-limiting.