Express the number as a product of its factors.

The factors of 99: 

99 = 1 × 99.

99 = 3 × 33.

99 = 9 × 11.

Factors of 99 are 1, 3, 9, 11, 33 and 99. Since the number has more than two factors, it is composite.

The number 99 is a composite number.