Methane
Methane is a gas with no color or smell that can burn and is found in nature and in waste.
Think of it this way
Picture a bin of old food scraps on a kitchen counter with a loose lid. As the scraps rot, tiny gas bubbles form and rise up through the pile. The bubbles float up, lift the lid, and drift into the air. You cannot see or smell them. Methane forms the same way — when plants or food break down without air, this light gas rises up and spreads out.
Explaining methane by grade level
When cow manure sits in a closed jar, tiny bugs eat it. As they eat, they make a gas you can not see or smell. That gas is called methane. You can burn it, just like the gas on a stove.