Which of the following compounds will react with ammoniacal cuprous chloride solution?
Correct: C
Ammoniacal cuprous chloride solution is a test for terminal alkynes (alkynes with a triple bond at the end of the chain, having an acidic hydrogen). Ethyne (acetylene) is a terminal alkyne and will form a red precipitate of cuprous acetylide. Other options are an alkane, an alkene, and another alkane, none of which react with this reagent.