Which of the following acids has the longest carbon chain among the first four members of the carboxylic acid series?

The correct choice highlights that butanoic acid has the longest carbon chain among the first four members of the carboxylic acid series. Carboxylic acids are organic compounds that contain a carboxyl functional group (-COOH) and are categorized based on the length of their carbon chains.

Methanoic acid, also known as formic acid, contains one carbon atom. Ethanoic acid, or acetic acid, has two carbon atoms. Propanoic acid, or propionic acid, consists of three carbon atoms. Butanoic acid, on the other hand, features four carbon atoms in its chain. Therefore, when comparing the length of the carbon chain in each of these acids, butanoic acid stands out as it has the most significant number of carbon atoms, indicating it has the longest carbon chain among the options provided.