When the Wh-family word (what, which, whose, how many, how much, etc.) is used before a noun to frame a question, it is called Interrogative Adjectives.
Examples:
- What profession are you in?
- Which river is the largest in the world?
- Whose car did you drive yesterday?
- How much money is needed to build a new house?
- By what time will you reach there?
In the above examples, What, Which, Whose, How much and By what appears before the nouns profession, river, car, money and time, respectively. Therefore, they are interrogative adjectives there.