Some odorless gases include ethane, helium, hydrogen, radon and nitrogen. Ethane is a flammable hydrocarbon made of two carbon atoms and six hydrogen atoms. The other gases are elements.
Nitrogen, like hydrogen, is found as two atoms in its free state. Normally it's inert, but when it's combined with other elements, it can become a powerful chemical, such as ammonia or nitroglycerine. It's also an excellent fertilizer. Some plants, such as beans, can fix nitrogen by taking it directly from the air, which is mostly nitrogen.
Being odorless is one of the properties that makes radon so dangerous. Radon, which is the heaviest gas, can collect in the basements, crawlspaces and lower floors of buildings and place the occupants in danger of lung cancer.
Hydrogen is the most abundant element in the universe and is crucial in providing fuel for main sequence stars, such as the sun. However, it is rather rare on Earth.
Helium is the first gas to be discovered in outer space. It was named after the sun god Helios because it was found on the sun. It is a noble gas, which means it doesn't react with other elements under normal conditions. Unlike hydrogen, helium is not flammable.