An interrogative sentence asks a direct question and always ends in a question mark:

Who can read this and not be moved?

How many roads must a man walk down?

Does money grow on trees?

Note that an indirect question does not make a sentence interrogative:

Direct/Interrogative

When was Lester Pearson prime minister?

Indirect/Declarative

I wonder when Lester Pearson was prime minister.

A direct question requires an answer from the reader, while an indirect question does not.