Correct Answer: 49

Solution : Let's check each option –
First option: 31 is divisible only by 1 and 31. So, it is a prime number.
Second option: 37 is divisible only by 1 and 37. So, it is a prime number.
Third option: 43 is divisible only by 1 and 43. So, it is a prime number.
Fourth option: 49 is divisible by 1, 7, 49. The number of factors of 49 is more than two. It is not a prime number.

Hence, the fourth option is correct.