In the skin of hippos, there is a type of natural sunscreen that contains the hypossudoric and nor-hypossudoric acids. Hypossudoric acid has a more...

In the skin of hippos, there is a type of natural sunscreen that contains the hypossudoric and nor-hypossudoric acids. Hypossudoric acid has a more effective protective action due to the greater amount of a certain group present in its molecule when compared to nor-hypossudoric acid, as observed in the following structural representations. The group responsible for the most effective protective effect is called:

The text presents two molecules and asks for the identification of the group responsible for the most effective protective effect.
a. Nitrile.
b. Hydroxyl.
c. Carbonyl.
d. Carboxyl.