In which of the following expressions, prime factorisation has been done?

(a) 24 = 2 × 3 × 4

(b) 56 = 7 × 2 × 2 × 2

(c) 70 = 2 × 5 × 7

(d) 54 = 2 × 3 × 9

Prime factorization is finding the factors of a number that are all prime.

(a) 24 = 2 × 3 × 4

As we can see in this factorization 4 is a composit number, so prime factorization has not been done.

(b) 56 = 7 × 2 × 2 × 2

Since all the factors are prime factors so, prime factorization has been done.

(c) 70 = 2 × 5 × 7

Since all the factors are prime factors so, prime factorization has been done.

(d) 54 = 2 × 3 × 9

As we can see in this factorization 9 is a composit number, so prime factorization has not been done.