Question

WHICH IS NOT CORRECT ABOUT SN2 ?
A) RATE OF SN2 IS DIRECTLY PROPORTIONAL TO THE DIELECTRIC CONSTANT OF THE MEDIUM
B) RATE OF SN2IS DIRECLTY PROPORTIONAL TO THE NATURE OF LEAVING GROUP
C) RATE OF SN2 IS INVERSELY PROPORTIONAL TO THE STERIC HINDERANCEPRESENT IN THE SUBSTRATE.
D) NONE OF THESE

Answer 1

SN2 reaction is fastest when polar aprotic solvent of low polarity is used.
If the dielectric constant is high, the polarity of the medium is high and rate of SN2 in this case will be less. 
If the leaving group of a reaction is good, it takes place faster.
SN2 involves backside attack of nucleophile on the substrate. So if there is stearic hindrance in the substrate, it becomes difficult for the nucleophile to come close and attack.
Hope it helps!