Nucleophilic substitution of the vinylic chloride shown follows an unusual two-step mechan...

Nucleophilic substitution of the vinylic chloride shown follows an unusual two-step mechanism. The nucleophile adds to the double bond in the first step; chloride ion is expelled in the second.

The measured value of ρ for the overall reaction is reported to be at least +4.5. Which is the most reasonable choice for the rate-determining step based on this information?

A. Step 1

B. Step 2