Definition:- Such sentences in which some question is asked are called Interrogative Sentences. There are two types of interrogative sentences.
W-Family:- Sentences start with when, where, why, what, whom, whose etc are called Interrogative Sentences with question words or W-family.
Helping Verb:- Sentences start with helping verbs like is, am, are, was, were, has, have, shall, will, can etc are called Interrogative Sentences with helping verbs.
Difference between W-Family and Helping Verb:- We need a complete sentence to answer a question with w-family on the other hand only the word 'Yes or No' is required to answer a question with helping verb.