Which LPG gas is commonly used for heating and cooking?

Propane is the correct answer because it is the most commonly used liquefied petroleum gas (LPG) for residential heating and cooking applications. It has a high energy content and burns cleanly, making it ideal for these purposes. Propane is favored in many regions, especially where natural gas lines are not available, as it can be easily transported and stored in tanks.

Butane and isobutane are also types of LPG but are generally preferred for specific applications like lighter fuel or portable cooking devices because they have a higher boiling point, which can make them less effective in colder climates where they may not vaporize as efficiently. Isobutylene is a different chemical altogether and is primarily used in industrial applications, such as producing synthetic rubber, rather than being a fuel source for heating and cooking. Thus, propane stands out as the primary choice for these residential applications.