The question is ambiguous.
A is right if the second hour is in terms of the original amount (16 grams). That is not how it should be done, but there is nothing in the problem restricting us from doing it that way.
B is right the way most people would do the problem. I would say you should accept this as the right answer. The 4.5% is taken away from what was left after the first hour. I would do it that way left to my own devices.
C. The % conversions are not correct. Those conversions are 35% and 45%
C is not even in contention for being right.
D Same problem as C