A concerto grosso is a multi-movement work for what instrument

A group of solo instruments called the concertino

Explanation:

It is generally a multi-movement work for a smaller group of solo instruments, called the concertino, contrasted with a larger group, called the ripieno. For example, In J. S. Bach's Fifth Brandenburg Concerto, the concertino is a flute, a violin, and a harpsichord.

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