Question

Which of the following is not a prime number?
$
  {\text{A}}{\text{. 2}} \\
  {\text{B}}{\text{. 3}} \\
  {\text{C}}{\text{. 4}} \\
  {\text{D}}{\text{. 5}} \\
 $

Answer 1

Hint: In this question we have to first write what is given to us or mentioned in the question. This will give us a clear picture of what our approach should be. In this question we have to use the definition of prime numbers and their properties.

Complete step-by-step answer:
It is given to us that we have to find which is not a prime number.
Well to answer the question we should first know about prime numbers. So those numbers who have two factors which are 1 and the number itself are called prime numbers. Now, looking at the question only 4 is the number which has 3 factors 1, 2, and 4 itself.
Hence, 4 is the answer and (C) is the correct option.

Note: In this question the first thing to know is what are prime numbers and their properties. By these basics you should be able to solve the question.