Which number is a prime number 14,13,21,33 ?

A prime number means that the number is only divisible by one and itself. 

14 is a multiple of 2 and 7, so 14 wouldn't be it.

21 is a multiple of 3 and 7, so 21 wouldn't be it.

33 is a multiple of 3 and 11, so 33 wouldn't be it.

13 is only divisible by itself because no number can be multiplied to get 13.

So the correct answer is : 13 is the prime number.

The answer you are looking for would be B. 13.

Prime numbers are numbers that are not divisible by any numbers except 1 and itself. All even numbers (except 2) are divisible by 2, therefore eliminating 14.
21 and 33 are both divisible by 3 (21/3 = 7 and 33/3 = 11). Thus making 13 the prime number.

I hope this helps!