Out of the four numbers listed, three are alike in some manner and one is different. Select the odd one.​​

Now, we check each options.

Option (a): 65 = 5 × 13

Option (b): 105 = 3 × 5 × 7

Option (c): 143 = 11 × 13

Option (d): 21 = 3 × 7

(65, 143, and 21) are all products of exactly two prime numbers.

105 is the only number that is a product of three prime numbers (3 × 5 × 7).

So, 105 is the only number that has three prime factors.

Thus, the correct answer is (b).