Hydrogen is a gas. It is lighter than air and it has no taste, odor, or color. There is a lot of hydrogen on Earth, but it is rarely found alone. Most of it is combined with other things. Hydrogen makes up part of water, petroleum, plants and animals, plastics, and other things of Earth.

Hydrogen is a gas. It is lighter than air and it has no taste, odor, or color. There is a lot of hydrogen on Earth, but it is rarely found alone. Most of it is combined with other things. Hydrogen makes up part of water, petroleum, plants and animals, plastics, and other things of Earth. Image to left: Hydrogen fuel powers U.S. space shuttles. Credit: NASA Hydrogen has many uses. Some industries use it in a process that makes metals pure. It is also a good fuel. The United States uses hydrogen fuel in its space shuttles. Some experimental cars use hydrogen fuel. Scientists are trying to find more ways to use hydrogen as an energy source. How to cite this article: To cite this article, World Book recommends the following format: "Hydrogen." The World Book Student Discovery Encyclopedia. Chicago: World Book, Inc., 2005.