Spot the Prime: Which Number Stands Alone With Limited Divisors?

To solve this problem, we will verify if each of the given numbers is a prime number. The numbers provided are $9$, $11$, $4$, and $6$.

• Option $9$: This number is not a prime because it has divisors other than 1 and itself; specifically, it is divisible by $3$ ($9 = 3 \times 3$).
• Option $11$: We need to check if $11$ is divisible by any number other than $1$ and $11$ itself, up to the square root of $11$ (approximately $3.32$). The integers to check are $2$ and $3$.

  $11$ is not even, thus not divisible by $2$.

  $11$ does not divide evenly by $3$ because $11 \div 3$ is not an integer.

  Since $11$ is not divisible by any number except $1$ and itself, it is a prime number.

• Option $4$: This number is not a prime because it is even, meaning it is divisible by $2$ ($4 = 2 \times 2$).
• Option $6$: This number is not a prime because it is divisible by $2$ and $3$ ($6 = 2 \times 3$).

Therefore, among the given options, the only prime number is $11$.