Find the missing number?

The missing number is 10.

The numbers in the sequence are all prime numbers, except for the missing number. The missing number must be a prime number that is less than 11, since the next number in the sequence is 11. The only prime number that is less than 11 is 10.

Here is a brief explanation of each option:

• Option A: 11 is not a prime number. It is a composite number.
• Option B: 10 is a prime number. It is the missing number.
• Option C: 7 is a prime number. It is not the missing number, because the missing number must be less than 11.
• Option D: 9 is not a prime number. It is a composite number.