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NEET levelSingle correct optionDifficulty 1 of 3o3010

In aqueous acetone, $(C X_{6} H X_{5}) X_{2} CH - Cl$ solvolyses by SN1. When some $LiCl$ is added to the solution, the observed rate of solvolysis

Adecreases slightly (common-ion effect)
Bincreases markedly
Cremains exactly unchanged under all conditions
Dbecomes second order in the substrate

Answer: A

The ionisation

R - Cl R X^{+} + Cl X^{-}

is reversible. Added chloride ion pushes the equilibrium back (and captures the cation), so fewer cations are converted to product and the net rate falls slightly. This is the common-ion (mass-law) effect typical of stable carbocations.

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