Question

Which of the following is not a prime number?

• A. 23
• B. 125
• C. 71
• D. 83

Answer 1

The correct option is B 125

Prime numbers are numbers which have only two factors, 1 and the number itself.
Visualising the given options
$23=1\times 23$
$125=1\times 125=1\times 5\times 25=1\times 5\times 5\times 5$
$71=1\times 71$
$83=1\times 83$
Clearly, 125 is not a prime number as it has more than two factors namely 1, 5, 25 and 125.