Which of the following is a prime number?

A prime number is defined as a natural number greater than 1 that cannot be formed by multiplying two smaller natural numbers. In other words, a prime number has exactly two distinct positive divisors: 1 and itself.

In this case, 11 fits the definition of a prime number. It is greater than 1 and can only be evenly divided by 1 and 11 without leaving a remainder. This means there are no other factors that can multiply together to yield 11.

On the other hand, the other numbers listed do not meet the criteria for being prime. The number 4 can be divided evenly by 1, 2, and 4, meaning it has more than two divisors. Similarly, 6 has factors of 1, 2, 3, and 6, and 9 can be divided by 1, 3, and 9. Each of these numbers has more than two divisors, confirming that they are not prime. Therefore, 11 stands out as the only prime number in the group.