The logic followed is:

All the given options except option (3) is a composite number whereas option (3) is a prime number.

Option 1: 15

It is a composite number.

Option 2: 27

It is a composite number.

Option 3: 37

It is a prime number

Option 4: 39

It is a composite number.

Hence, the correct answer is "37".

• Some facts about the Prime numbers:
• A prime number is a natural number greater than 1 that is not a product of two smaller natural numbers.​
• The only even prime number is 2. All other even numbers can be divided by 2.
• If the sum of a number's digits is a multiple of 3, that number can be divided by 3.
• No prime number greater than 5 ends in a 5. Any number greater than 5 that ends in a 5 can be divided by 5.
• Zero and 1 are not considered prime numbers.
• Except for 0 and 1, a number is either a prime number or a composite number. A composite number is defined as any number, greater than 1, that is not prime.
• Prime no between 1 to 100 are 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97.