Determine the molecular formula of an unknown hydrocarbon. 15 cm3 of a gaseous hydrocarbon was completely combusted with 95 cm3 (an excess) of oxygen. After cooling to room temperature, the residual gaseous products (carbon dioxide and excess oxygen) occupied a volume of 80 cm3. On adding aqueous sodium hydroxide to remove CO2, the volume decreased to 50 cm3. Determine the molecular formula of the hydrocarbon.