The correct answer is C. Ethyne.
An alkyne is an unsaturated hydrocarbon with a triple bond between two carbon atoms. The general formula for an alkyne is $C_nH_{2n-2}$. The first member of the homologous series of alkynes is ethyne, which has the chemical formula $C_2H_2$. It is also known as acetylene. Ethyne is a colorless, flammable gas with a characteristic garlic-like odor. It is used as a fuel in welding and cutting torches, and as a precursor to other chemicals, such as ethylene and acetaldehyde.
Methane, ethane, and propane are all alkanes, which are saturated hydrocarbons with no double or triple bonds. Methane has the chemical formula $CH_4$, ethane has the chemical formula $C_2H_6$, and propane has the chemical formula $C_3H_8$. Alkanes are typically nonpolar and have low boiling points. They are used as fuels, solvents, and lubricants.