Hello,

Good question - the logic behind why is a bit beyond the scope of the MCAT, so I will give you the crux of the matter first, work through the question second, and explain briefly how this might work third.

1. When you're looking for things that absorb light on the MCAT, look for conjugated pi systems.

2. That being said, this is a significantly more complicated question (and one I suspect most students won't get) because three of your answer choices (B-D) fit this description. Honestly, guessing on this question is a great thing to do, and it is great that this is your first instinct!

This probes a more advanced concept known as push-pull chromaphores. I would expect to get more context on a passage containing this type of question.

The way I could eliminate an answer on this particular question is by looking at C and D, as they say opposite things. If you draw an aromatic amine, you can see it donates electron density by resonance, while a carbonyl will withdraw electron density (See photo link below)
. This eliminates D, as it states amines are electron withdrawing, which is false.
From here, you have a 50/50 shot between B and C, which is the best outcome I would expect for this question.

https://ibb.co/vHrcN4N (I have drawn a carboxylic acid, not a carbonyl here, but both carboxylic acids and carbonyls withdraw electron density) I have also not drawn melanin itself, but a significantly simpler structure exhibiting the basics of what the question is getting at.

3. You haven't provided me with the answer, but I'm pretty sure C is correct because it is what we call a push- pull chromaphore (Please correct me if I'm wrong). The physical chemistry behind why a push pull chromaphore absorbs over a wider range is complicated, still under review, and a complete explanation is beyond my understanding.

The short form that I kind of think about to help me remember is shown in the image link I have provided - when you have an electron donating group and an electron withdrawing group on the same aromatic system, you can access a resonance hybrid which will absorb at more a larger variety of wavelengths because it has access to a larger number of absorptive states. Again - this might not be the most accurate answer, as I'm not well versed enough in physical chemistry to explain why, but I hope it helps a little bit (even if what you get is that this is a tough question which is best to guess).