Q.9. 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

(a) 24 = 2 x 3 x 4
Here, 4 is not a prime number.
Hence, it is not a prime factorisation.
(b) 56 = 7 x 2 x 2 x 2
Here, all factors are prime numbers
Hence, it is a prime factorisation.
(c) 70 = 2 x 5 x 7
Here, all factors are prime numbers.
Hence, it is a prime factorisation.
(d) 54 = 2 x 3 x 9
Here, 9 is not a prime number.
Hence, it is not a prime factorisation.