Right option is (a) Natural gas
To elaborate: Natural gas is found dissolved in petroleum under earth’s surface in oil and gas bearing areas. It mainly contains 85% Methane (CH4) and hydrogen (H2) along with small percentages of ethane and ethylene. Liquefied petroleum gas (LPG) is a mixture of propane, butane and other hydrocarbons separated from natural gas. It is stored under pressure in the liquid form. It is used as a domestic fuel and as an automobile fuel.