Step 1: Look at the list of numbers: 2, 3, 5, 7, 9, 11.
Step 2: Understand what a prime number is. A prime number is a number greater than 1 that has no positive divisors other than 1 and itself.
Step 3: Check each number in the list to see if it is prime.
Step 4: 2 is prime (only divisible by 1 and 2).
Step 5: 3 is prime (only divisible by 1 and 3).
Step 6: 5 is prime (only divisible by 1 and 5).
Step 7: 7 is prime (only divisible by 1 and 7).
Step 8: 9 is NOT prime (it is divisible by 1, 3, and 9).
Step 9: 11 is prime (only divisible by 1 and 11).
Step 10: Since 9 is the only number that is not prime, it is the odd one out.
Prime Numbers – A prime number is a natural number greater than 1 that cannot be formed by multiplying two smaller natural numbers. The only divisors of a prime number are 1 and itself.