What is interrogative pronoun

An interrogative pronoun is a questioning pronoun, used when asking. For instance the five Ws - who, what, where, when, why. In this sentence - How could that be you moron? - the interrogative pronoun is 'How'.

It refers to a pronoun that introduce a question. (who, whom, whose, which and what) function as interrogative pronouns

"Who are you?'

"I don't know,' she said."