Answer: the functional group
Step-by-step explanation:
Functional groups are specific group of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules.
1. Esters have functional group
.
Example: methyl ethanoate with molecular formula
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2. Alcohols have functional group
.
Example: Propanol with molecular formula
3. Aledydes have functional group
.
Example: propanal with molecular formula
Thus esters , alcohols and aldehydes may have same number of carbon atoms and similar branching pattern but different functional groups.