Rate-determining step, Haloform reaction

Having established that there is a pre-equilibrium between haloforms and trihalocarbanions, the rate-determining step of the over-all hydrolysis remains to be located among the subsequent reactions of the trihalocarbanions. Two mechanisms are compatible with the observed kinetics viz. 

Problem 9.3. The following experimental observations have been made with respect to the representation of the h oform reaction shown in Scheme 9.9 and other such base-catalyzed haloform processes (a) the rate of disappearance of starting ketone is independent of both the concentration and nature (Cl, Br, or I) of the hypohalite used, and (b) as long as the solution remains basic and there is sufficient halogen present, the reaction will continue until all of the starting ketone is consumed. Formulate a rate expression for what you believe to be the rate-determining step in Scheme 9.9 and that is consonant with the observations. 

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