What is the prefix that indicates a hydrocarbon chain with two carbon atoms?

The prefix that indicates a hydrocarbon chain with two carbon atoms is "Eth-." In organic chemistry, the naming of hydrocarbons follows a systematic nomenclature where each prefix corresponds to a specific number of carbon atoms in the chain.

For aliphatic hydrocarbons:

• "Meth-" is used for one carbon atom.

• "Eth-" is used for two carbon atoms.

• "Prop-" is for three carbon atoms.

• "But-" is for four carbon atoms.

Thus, "Eth-" correctly identifies a hydrocarbon structure known as ethane for a chain with two carbon atoms. This systematic naming is crucial in understanding and communicating the structure of organic compounds effectively.