# In which of the following case increase in solvent polarity causes a large in rate of the reaction.

a.$R-X+Nu^-$------->

b.$R-X+Nu$----------->

c.$R^--X^++Nu^-$------->

d.$R^--X^++Nu$--------->

As the reactants are neutral the transition state will be charged and the transition state complex is more stabilized in comparison to substrate solvent of increased polarity and so increased rate .