Interrogative adjectives indicate a quality or indefinite quantity and come with specific nouns. The most common forms are che (what? what kind of?), quale (which?), and quanto (how much? how many?). For example:
Quali parole ricordi? (Which words do you remember?)
Che libri leggete? (What books do you read?)
Quante ragazze vengono? (How many girls are coming?)
Che ora è? (What time is it?)
Quanto pane vuoi? (How much bread do you want?)
Notice the difference in meaning between che and quale. The question Quali film hai visto? asks "Which films have you seen?" (For example, Il Postino, Ciao Professore! or La Vita è Bella.) The question Che film hai visto? asks "What types of films have you seen?" (For example, comedy, romance, or thriller.)
The interrogative adjective quanto (how many, how much) agrees in number and gender with the noun it modifies and has four forms (see table below).
FOUR FORMS OF QUANTO? (HOW MUCH?/HOW MANY?
masculine/singular
quanto
Quanto tempo fa? (How long ago?)
masculine/plural
quanti
Quanti anni hai? (How old are you?)
feminine/singular
quanta
Quanta farina c’è? (How much flour is there?)
feminine/plural
quante
Quante studentesse ci sono? (How many students are there?)