What are the two main types of gas used in appliances?

Natural gas and propane are indeed the two primary gases commonly used in residential and commercial appliances. Natural gas, primarily composed of methane, is widely supplied through pipelines and is used for heating, cooking, and hot water in many regions. It is advantageous due to its abundance, lower cost, and convenience of supply.

Propane, on the other hand, is often used where natural gas is not available, such as in rural areas, and is stored in tanks for use in heating, grilling, and other applications. It can be easily transported and is efficient for residential heating and cooking.

These two gases cover a broad range of usage in appliances, making them the most relevant choices for this question. Other options, including hydrogen, butane, and methane, either reflect less common usage or specific conditions that do not apply broadly across typical gas appliances.