Final answer:
The number 9 is composite because it has more than two factors: 1, 3, and 9 itself. The other numbers listed (2, 11, and 5) are prime, as they can only be divided evenly by 1 and the number itself.
Step-by-step explanation:
To determine which number is composite, we need to understand what a composite number is. A composite number is a number that has more than two factors, which means it can be divided evenly by at least one other number besides 1 and itself. Looking at the options - 2, 11, 5, and 9, we can evaluate each one.
Number 2 is a prime number because it can only be divided by 1 and itself. Similarly, number 11 and number 5 are also prime numbers. However, the number 9 can be divided evenly by 1, 3, and 9, which makes 9 a composite number.