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Which of the following is a prime number?

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answer is D.

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Detailed Solution

We have to find which one is the prime number.
A number is a prime number when it has only 2 factors i.e., 1 and the number itself.
We can write 81 as -

81 = 3 × 27

, which means it has more than 2 factors, so 81 is not prime.
We can write 87 as –

87 = 3 × 29

, which means it has more than 2 factors, so 87 is not prime.
We can write 91 as –

91 = 7 × 13

, which means it has more than 2 factors, so 91 is not prime.
But we cannot write 97 as the product of 2 numbers other than 1 and 97.

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