Which gas is lighter than air and often used in heating applications?

The gas that is lighter than air and commonly used in heating applications is natural gas. Natural gas primarily consists of methane, which has a lower density than air, allowing it to rise when released into the atmosphere. This property makes it suitable for heating applications, as it can be distributed effectively through pipelines and used in appliances such as furnaces and water heaters.

While butane, propane, and ethane are also used as fuels, they are heavier than air. Butane and propane are typically stored as liquids in pressurized containers and, when released, tend to settle in low-lying areas, which can pose safety risks. Ethane, while primarily of interest as a petrochemical feedstock, is also heavier than air and not a common heating fuel. Thus, the correct answer focuses on natural gas, which is the most prevalent and suitable option for heating applications.