H4C2 is organic compound named 'Ethylene'! It contains two carbon atoms which have two hydrogen atoms bonded to each carbon! It is gas at room temperature!
Methane
Based on the naming rules for acids. This would be just hydrogen and carbon. H2C or H4C. BUT.. I do not know if this exists in nature, since carbon tends to form covalent bonds with hydrogen, not ionic. CH4 is methane, and CH2 is acetylene.