What is the name for a 3-carbon chain with a methyl group on the second carbon?

The correct name for a 3-carbon chain with a methyl group on the second carbon is 2-Methylpropane. In the IUPAC nomenclature system, the primary chain is identified first, which is a straight-chain alkane with three carbon atoms, known as propane. When substituents, such as a methyl group, are present, the position of these groups is indicated by numbering the carbon atoms in the main chain.

In this case, the main chain (propane) consists of three carbon atoms, which are numbered from one end to the other. The methyl group is attached to the second carbon, thus the compound is named 2-Methylpropane. The prefix "2-" indicates the methyl group's position on the second carbon of the propane chain.

This nomenclature is based on both the length of the carbon chain and the position of the substituent, making 2-Methylpropane the appropriate name for this structure.