OpenStudy (anonymous):

hydrocarbon = only carbon and hydrogen C = 12 g/mol H= 1 g/mol $$\large C_xH_y$$ The formula needs to make sense, so lets try 5 carbons 5 C = 60 12 H = 12 |dw:1412381545155:dw| pentane fits 6 C = 72; doesnt work 4 C = 48 72-48= 24 H's; doens't make sense Pentane is the only possible formula