The correct answer is option 'A' - Butane and Propane.

L.P.G. stands for Liquefied Petroleum Gas. It is a flammable hydrocarbon gas that is commonly used as a fuel in various applications. L.P.G. is primarily composed of two main hydrocarbons, namely butane and propane.

Here is a detailed explanation of the two main hydrocarbons present in L.P.G.:

1. Butane:
- Butane is an organic compound with the molecular formula C4H10. It is an alkane belonging to the family of saturated hydrocarbons.
- It exists in various forms, including n-butane and isobutane. In L.P.G., n-butane is the most commonly used form.
- Butane is a colorless gas at room temperature and is commonly used as a fuel for heating, cooking, and camping stoves.
- It is easily liquefied under moderate pressure, which allows it to be stored and transported in its liquid form. This property makes butane suitable for use in L.P.G. cylinders.

2. Propane:
- Propane is also an organic compound with the molecular formula C3H8. It is also an alkane and belongs to the family of saturated hydrocarbons.
- Propane is a colorless and odorless gas at standard temperature and pressure. It is derived from natural gas processing and petroleum refining.
- Similar to butane, propane can be easily liquefied under moderate pressure, making it suitable for storage and transportation purposes.
- Propane is widely used as a fuel for heating, cooking, and as an alternative fuel for vehicles. It is also used in industrial processes, such as metal cutting and welding.

In summary, the two main hydrocarbons present in L.P.G. are butane and propane. These hydrocarbons have similar properties and are commonly used as fuels due to their high energy content and ease of liquefaction.