Question

which of the following is a nucleophile? 1) H2O 2) SO3 3) ALCL3 4) BF3..

Answer 1

A nucleophile is a species which is rich in electron. Therefore it attacks the electron deficient areas.The species which have an extra lone pair can be considered as a nucleophile. Here H2O is having two lone pairs while the lewis bases like BF3 and AlCl3 are electron deficient as their octet is incomplete. therefore They CANNOT act as a nucleophile. while SO3 can neither act as an electrophile or nucleophile.but in aq medium it can act as a nucleophile coz of SO3- ions.

Answer 2

Nucleophile are the species which are electron rich center .
So among them the the nucleophile is SO3