Interrogative pronouns are pronouns that are used to ask questions. They include what, which, who, whom, and whose.
What is used to ask about a thing or an animal from an unspecified number of options.
What is your favourite colour?
Which is used to ask about a thing or an animal from a limited number of options.
Which is your favourite colour: red or blue?
Who is used to ask about the person who is the subject of the sentence/the person who performs an action.
Who was it?
Whom is used to ask about the person who is the object of the sentence.
To whom did you write?
Whose is used to ask about the owner of something.
Whose is that house?