Answer : The correct option is, (4) an ester.
Explanation :
As we know that an organic acid is an organic compound that has the properties of an acid. For example : Acetic acid.
And the alcohol is an organic compound that contains one or more hydroxyl groups attached to a carbon atom. Fro example : Ethanol.
When an organic acid react with an alcohol the it produces an ester.
For example : when an organic acid (acetic acid) react with an alcohol (ethanol) to gives an ester (methoxyethane).
The balanced chemical reaction will be,
Hence, the reaction between an organic acid and an alcohol produces an ester.