Question

Which of the following numbers are prime ?

• A. $5$
• B. $72$
• C. $97$
• D. $1$

Answer 1

Answer: (A), (C)

The correct options are
A $5$
C $97$

$5$ has only two factors i.e. $1$ and $5$. So, it is prime.

$72$ is an even number and we know that no other even number except $2$ is prime. So, it is not prime.

Nearest greatest square root of $97$ is $10$.
Now, checking divisibility with prime numbers which are less $10$ i,e, $2,3,5,7.$
Since, $97$ is not divisible by any above numbers. So, it is prime.

$1$ is neither prime nor composite.