Which prefix denotes a hydrocarbon chain with seven carbon atoms?

The prefix that denotes a hydrocarbon chain with seven carbon atoms is "hept-." In organic chemistry, prefixes are used to indicate the number of carbon atoms in the longest continuous chain of a hydrocarbon. The prefix "hept-" is derived from the Greek word "hepta," meaning seven.

To provide context, "pent-" refers to five carbon atoms, "hex-" refers to six carbon atoms, and "oct-" refers to eight carbon atoms. Each of these prefixes is used to name hydrocarbons based on the number of carbon atoms present in the main chain. Therefore, "hept-" is specifically associated with a chain of seven carbon atoms, making it the correct choice.