The logic followed is:

Petrol, Diesel, and Kerosene are used as liquid fuels.

While;

LPG is used as a gas fuel.

Hence, "LPG" is the correct answer.

1) Petrol: 

Gasoline or petrol is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines. Petroleum is formed when large quantities of dead organisms–primarily zooplankton and algae–underneath sedimentary rock are subjected to intense heat and pressure.

2) Diesel: 

Diesel fuel, in general, is any liquid fuel specifically designed for use in diesel engines. Diesel engines are more efficient than gasoline engines. At high altitudes, diesel engines get better power than gasoline.

3) Kerosene: 

Kerosene, also known as paraffin, is a combustible hydrocarbon liquid that is derived from petroleum. It is widely used as a fuel in aviation as well as households. Kerosene is less volatile than gasoline. Its flash point (the temperature at which it will generate a flammable vapour near its surface) is 38 °C (100 °F) or higher, whereas that of gasoline is as low as −40 °C (−40 °F). This property makes kerosene a relatively safe fuel to store and handle.

4) LPG: 

Liquefied petroleum gas (LPG), is a flammable mixture of hydrocarbon gases such as propane and butane. LPG is used as fuel gas in heating appliances, cooking equipment, and vehicles.