Methane is a colourless, odourless, non-toxic but flammable gas. What is its common name?

Marsh gas

The correct answer is option 3. Marsh gas.

Methane, which is a colorless, odorless, non-toxic, but flammable gas, is commonly known as marsh gas. It earned this name because it is often produced naturally in marshes, wetlands, and other environments where organic matter decomposes in the absence of oxygen, a process known as anaerobic decomposition.