'which' is a pronoun 1. Which of these do you want? Which one do you want? 2. Whichever: Choose which appeals to you. 3. (used relatively in restrictive and nonrestrictive clauses to represent a specified antecedent): Example:The book, which I read last night, was exciting. The socialism which Owen preached was unpalatable to many. The lawyer represented five families, of which the Costello family was the largest. 4. (used relatively in restrictive clauses having that as the antecedent): Damaged goods constituted part of that which was sold at the auction. 5. (used after a preposition to represent a specified antecedent): the horse on which I rode.

Who is the subjective. Who is the man standing there? Whose is possessive.(of who) Whose jacket is this? Whom is objective. Whom did you write a letter to./To whom did you write a letter? (Not who in this instance because the 'who' is an object of an action.