Consider the following `S_(N^2)`j reactions
I. `RX+Y^(-)toR-Y+X^(-)`
II. `RX+Y^(-)toR-Y^(+)+X^(-)`
III. `RX^(+)+Y^(-)toR-Y+X`
IV. `RX^(+)+YtoR-Y^(+)+X`
In which reactions there is large increase and large decrease in rate of reaction respectively with increase in polarity of the solvent.

Options

A. II and III
B. II and IV
C. I and IV
D. IV and I

Answer

A

Explanation

For II. Transition state is more stabilised than reactant.
For III : Reactants are more stabilised than transition state. Hence, rate of reaction is affected accordingly.