Prime numbers in 1-100 range are: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97.

We can see that all the numbers in options (A), (B), and (C) are prime numbers.

However, number 91 in option (D) is not a prime number. As, $91 = 13 \times 7$. So, this group is different from the others.

Hence, option (D) is correct.