To determine whether a number is composite or not, we need to understand the concept of composite numbers. A composite number is a positive integer greater than 1 that has factors other than 1 and itself. In other words, it can be divided by numbers other than 1 and itself without leaving a remainder.

Let's analyze the given options:

a) 21: We can find factors of 21 by dividing it by numbers from 2 to 10. It is divisible by 3 and 7, so it has factors other than 1 and itself. Therefore, 21 is a composite number.

b) 27: We can find factors of 27 by dividing it by numbers from 2 to 13. It is divisible by 3 and 9, so it has factors other than 1 and itself. Therefore, 27 is a composite number.

c) 39: We can find factors of 39 by dividing it by numbers from 2 to 19. It is divisible by 3 and 13, so it has factors other than 1 and itself. Therefore, 39 is a composite number.

d) 11: To determine if 11 is a composite number, we need to check if it has any factors other than 1 and itself. When we divide 11 by numbers from 2 to 10, we find that it is not divisible by any of them. Therefore, 11 does not have any factors other than 1 and itself, making it a prime number. Hence, option D is the correct answer as it is not a composite number.

e) None of these: This option is incorrect because option D, which states that 11 is not a composite number, is the correct answer.

In conclusion, the number that is not a composite number among the given options is 11 (option D).

What is the answer