[kelaklub]

The answer to the following question is stated as choice D. But couldn't choice E be just as valid an answer? Thanks.

[wereworm73]

Nope, S_N2 will occur in a wide variety of solvents, but the key to the reaction is to have a strong nucleophile. 

[plu]

S_N2 reactions are favoured in polar aprotic solvents, in which the attacking nucleophile is not solvated (thus raising its energy and increasing its tendency for attack) but the carbocation species is (it is stabilized).

[Donaldson Tan]

SN2 depends on nucleophile strength and E2 depends on the basic character.

To favour SN2, the basic character somehow must be suppressed, yet at the same time improve the nucleophilic strength.

[mkaplan4]

aprotic solvents are best since they do not form strong interactions with the nucleophile, thus decreasing its nucleopholicity.

[Will]

S_N2 reactions are favoured in polar aprotic solvents, in which the attacking nucleophile is not solvated (thus raising its energy and increasing its tendency for attack) but the carbocation species is (it is stabilized).

In E2 you don't have a carbocation species (as far as I know), I think you are thinking of E1 (except E1cB) where you get a cation intermediate (which doesn't have to be carbon; it can be nitrogen or oxygen for example).