Which of the following is a prime number?

A prime number is defined as a natural number greater than 1 that has no positive divisors other than 1 and itself. This means that a prime number can only be divided evenly by 1 and the number itself, resulting in a whole number.

In this case, 11 fits the definition of a prime number because it can only be divided evenly by 1 and 11. It does not have any other divisors, confirming its status as prime.

On the other hand, the other numbers listed have multiple divisors. For instance, 4 can be divided by 1, 2, and 4; 6 can be divided by 1, 2, 3, and 6; and 15 can be divided by 1, 3, 5, and 15. Thus, only 11 is a prime number among the choices provided.