Which compound type contains a carbonyl group bonded to two carbon atoms?

The correct choice is ketone, which is defined by having a carbonyl group (C=O) that is bonded to two carbon atoms. In a ketone, the carbonyl group is situated between two other carbon chains or groups, which distinguishes it from other types of carbonyl-containing compounds. This structural feature is essential to its classification; in a ketone, there are no hydrogens directly attached to the carbonyl carbon, unlike in aldehydes.

In contrast, aldehydes feature a carbonyl group bonded to at least one hydrogen atom and thus are typically found at the end of carbon chains. Carboxylic acids contain a carbonyl group bonded to a hydroxyl group (-OH), while esters consist of a carbonyl group adjacent to an ether-like group (-O-). The specific bonding pattern of the carbon atoms in ketones is what makes them unique among these various organic compounds.