Questions & Answers about Cette pièce est calme.
Because pièce is a feminine singular noun.
French demonstratives change to match the noun:
- ce = masculine singular
- cet = masculine singular before a vowel or mute h
- cette = feminine singular
- ces = plural
So:
- ce livre = this book
- cet hôtel = this hotel
- cette pièce = this room
- ces livres = these books
Since pièce is feminine, cette is the correct form.