What is the IUPAC name for CH3CHO?

The IUPAC name for CH3CHO is ethanal, and this designation comes from the composition and structure of the molecule itself. Ethanal is the simplest aldehyde, defined by the presence of a carbonyl group (C=O) at the end of a carbon chain. In this case, CH3CHO can be broken down into its components: it contains two carbon atoms (indicated by "eth" from ethane) and the functional group of an aldehyde (indicated by the suffix "al").

The structure consists of a methyl group (CH3-) bonded to a carbonyl group (C=O) and a hydrogen atom, which is characteristic of aldehydes. This is why the correct IUPAC name is ethanal.

In contrast, other options do not correctly describe the compound's structure. Butanoic acid, for example, contains four carbon atoms with a carboxylic acid group (COOH), and acetone is a ketone with a three-carbon structure featuring a carbonyl group in the middle rather than at the end. Propanal, while also an aldehyde, consists of three carbon atoms, not the two present in CH3CHO. Thus, ethanal is the correct