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 (without leaving a remainder) by 1 and the number itself.

When evaluating the options, 1 is not considered a prime number because it does not meet the criterion of being greater than 1. The number 4 has divisors other than 1 and itself (specifically, it can be divided by 2), which means it cannot be classified as prime. The number 9 also has divisors other than 1 and itself (for example, it can be divided by 3), ruling it out as a prime.

On the other hand, the number 7 fits the definition of a prime number. Its only divisors are 1 and 7, satisfying the requirement of having no other divisors. Thus, 7 is indeed a prime number.