What is the smallest unit of most compounds?
Compounds are multiple things of something like molecules, such as salt. Salt is sodium and chloride. So sodium and chloride are the smallest unit. Though it can be atoms because everything is made of atoms. Sodium and chloride is also elements, and the both form molecules. These many molecules make salt.
A compound is a substance that consists of two or more elements which have undergone a chemical reaction in its formation. After the chemical reaction, a compound cannot be broken down into its components by physical means.
The smallest distinguishable unit of the compound is the molecule resulting from the reaction.