ANS:A - carboxylic acid

An ester is formed when an alcohol reacts with a carboxylic acid in the presence of an acid catalyst. This reaction is known as esterification and involves the condensation of the alcohol's hydroxyl group (-OH) with the carboxyl group (-COOH) of the carboxylic acid. The reaction typically occurs under acidic conditions, and a small amount of acid catalyst, such as sulfuric acid or hydrochloric acid, is often used to facilitate the reaction. The general chemical equation for the esterification reaction between an alcohol (R-OH) and a carboxylic acid (RCOOH) is as follows: R-OH+RCOOH→R-COO-R’+H2OR-OH+RCOOH→R-COO-R’+H2​O In this reaction, the hydroxyl group (-OH) of the alcohol reacts with the carboxyl group (-COOH) of the carboxylic acid to form an ester (R-COO-R') and water (H2O) as a byproduct. Therefore, the correct answer is: carboxylic acid.