The correct answer is Ethanol.
Ethanol is a flammable liquid that is added to domestic LPG cylinders to help in the detection of gas leakage. It has a strong, unpleasant odor that can be easily detected by humans. When ethanol is released into the air, it will quickly evaporate and form a cloud that can be seen. This makes it easy to identify any leaks in an LPG system.
Methanol, ethanol, and chloroform are all organic compounds that are commonly used in industrial and commercial applications. However, only ethanol has the properties that make it suitable for use in domestic LPG cylinders. Methanol is a highly flammable liquid that can be easily ignited by a spark or flame. Chloroform is a toxic chemical that can cause serious health problems if inhaled. Thioethanol is a less common compound that is not typically used in domestic LPG cylinders.
In conclusion, ethanol is the only agent among the options that is added to domestic LPG cylinders to help in the detection of gas leakage. It is a flammable liquid that has a strong, unpleasant odor that can be easily detected by humans. When ethanol is released into the air, it will quickly evaporate and form a cloud that can be seen. This makes it easy to identify any leaks in an LPG system.