Correct option is B
The given series: 16, 17, 20, 21, 24, ?
Logic; alternating between adding 1 and 3.
16 + 1 = 17
17 + 3 = 20
20 + 1 = 21
21 + 3 = 24
Now, following this alternating pattern, we add 1 to 24:
24 + 1 = 25
So, the next number in the series is 25.
Thus, the correct answer is (B) 25.