Which section is not one of the four groups in the orchestral palette?

The choices for the above question are:
A. strings
B. voice
C. brass
D. percussion

The answer to your question is: B. voice. An orchestral piece, such as a symphony or a concerto, will always have strings, brass, and percussion.  I hope that this is the answer that you were looking for and it has helped you.

Contemporary jazz is sometimes called smooth jazz

Did you read the book