How do Lasius niger, the common black garden ants, use hydrocarbons to communicate?

Hydrocarbons are chains of Carbon atoms populated with Hydrogen atoms. When combusted with oxygen, carbon dioxide and water are produced. You know most of them as alkanes; the lowest molecular weight members being methane, ethane, propane, butane, hexane, heptane, and octane.

When you add other elements (Nitrogen, Phosphorus, Sulfur, etc.), it is no longer known as a hydrocarbon, takes on a different 3-dimensional shape, and has very different chemical properties.

The only hydrocarbon I know of, for certain, that animals make is methane; and that is generally made by bacteria that live inside the animals' guts.

I do not know of any true hydrocarbons, other than possibly methane, that ants produce and use for communication.

What is a question you could ask to tell if someone's a sociopath?

By definition, sociopaths are highly skilled and almost intuitive on the tricks that can be played.
So, any question (just one question) would be a high suspect. What makes you think that a pro in this game cannot see through your attempt to outsmart him/her?

I suggest that you familiarize yourself with the condition (below response details the latest research on it).
Once you are done with that, and if you are still dead set on seeking out that one question, you must add more context to your question (describe the situation/person you're facing) to get a tailored response.

Margaret Weiss' answer to Sociopathy: Can sociopaths act kindly?