There are only five main interrogative pronouns, all of which begin with –wh: who, whom, whose, which, and what. Each of these pronouns is used when asking a specific question. They are only used to ask questions and not for any other grammatical constructions. However, the five pronouns can also be used in sentences. As long as they are not used in questions, they are not interrogative pronouns.
Out of the five interrogative pronouns, only who and whom refer to people while which and what are used for things. These pronouns do not have gender. The other pronouns considered as interrogative pronouns are whatever, whoever, whomever, and whichever.
We use interrogative pronouns when we need to know something – something that we have no knowledge of. There are other words beginning with –wh and we should not confuse them with the interrogative pronouns as they are not. The words are when, where, and why. Unlike other pronouns, the interrogative pronoun does not have an antecedent as the antecedent is unknown.
Using the five interrogative pronouns.
Interrogative pronouns have three cases
The Interrogative pronouns can be used in the subjective, possessive, and objective cases..
'Who' may be used as an object
‘Whom’ cannot be used as the subject.
Whom can be used only as an object
Preposition can be placed in front of interrogative pronoun ‘whom’
Other interrogative pronouns:
whatever, whoever, whomever, and whichever.