Answer:
The functional group is called an amide. This is option C.
Explanation:
We see this is a three-carbon chain (a propyl chain), that ends with a double bond to oxygen and a single bond to an amine group (NH2). If the end carbon were only bound to the NH2 group and 2 hydrogen atoms, it would be an amine. If the end carbon only had a double bond to oxygen and a single bond to hydrogen, it would be an aldehyde. However, when a terminal carbon (a carbon at the end of a chain) has both a double bond to oxygen, and a single bond to an amine (NH2), it is called an amide.
We can also discount the answer thiol right away because those have a carbon-sulfur bond, and there is no sulfur in this molecule.
