Which one of the following acids is the second member of the carboxylic acids series?

The second member of the carboxylic acids series is ethanoic acid. Carboxylic acids are a family of organic compounds that contain a carboxyl group (-COOH). The naming of carboxylic acids is based on the number of carbon atoms present in the longest chain.

In this series, methanoic acid, which has one carbon atom, is the first member. Ethanoic acid, with two carbon atoms, follows as the second member. Propanoic acid has three carbon atoms and is the third member, while butanoic acid contains four carbon atoms, making it the fourth in the series.

This sequence of carboxylic acids can be illustrated as follows: methanoic acid (1 carbon) → ethanoic acid (2 carbons) → propanoic acid (3 carbons) → butanoic acid (4 carbons). Therefore, the correct answer reflects the proper order of these compounds in the context of their carbon chain length.