Which of the following is a prime number?

A prime number is defined as a natural number greater than one that has no positive divisors other than 1 and itself. In simpler terms, a prime number is one that cannot be formed by multiplying two smaller natural numbers.

The number 7 fits this definition perfectly since its only divisors are 1 and 7. It cannot be divided evenly by any other integers, qualities that meet the criteria for prime numbers.

In contrast, the number 1 is not considered prime because it does not meet the requirement of being greater than one. The number 4 has divisors of 1, 2, and 4, indicating that it can be divided by numbers other than itself, which disqualifies it as a prime number. Lastly, 9 is divisible by 1, 3, and 9, meaning it also fails to fit the definition of a prime number due to having more than two divisors. Thus, the only prime number listed is 7.