Which type of music is written for and performed by a small ensemble
symphony
chamber
piano sonata
opera

Chamber.

Explanation:

Chamber music is written for a small ensemble or a group that could fit in a large room.

It could not be the other options, because,

1. A symphony is a large group of instruments.

2. A piano sonata is performed by a soloist.

3. An opera is not performed by an ensemble.

Hope this helps!