Choose the correct option

Which of the following groups of numbers are all prime numbers?

(a) 2, 5, 15, 19  (b) 3, 11, 23, 31 (c) 2, 3, 5, 9 (d) 7, 17, 29, 49

Prime numbers are the numbers that have only two factors, that are, 1 and the number itself.

Answer: Option (b) 3, 11, 23, 31 is the group containing all the prime numbers.

Let's identify the prime numbers out of the given numbers.

Explanation:

Let us examine each group:

• 2, 5, 15, 19 ------> 2, 5, 19 are prime but 15 = 3 × 5 is composite
• 3, 11, 23, 31 ------> all are prime numbers
• 2, 3, 5, 9 --------> 2, 3, 5 are primes but 9 = 3 × 3 is composite.
• 7, 17, 29, 49 --------> 7, 17, 29 are primes but 49 = 7 × 7 is composite.

Thus, option (b) 3, 11, 23, 31 is the group containing all the prime numbers.