What is the prefix for a carbon chain of four?

The prefix for a carbon chain of four is "but-". In organic chemistry, prefixes are used to indicate the number of carbon atoms in the longest continuous chain of a hydrocarbon. Each prefix corresponds to a specific number of carbons: "meth-" for one carbon, "eth-" for two, "prop-" for three, "but-" for four, "pent-" for five, and "hex-" for six.

Thus, since a chain with four carbon atoms is designated as "butane" in its alkane form, the "but-" prefix accurately reflects this structure. Understanding these prefixes is essential for correctly naming and recognizing hydrocarbons in various chemical contexts.