Hydrogen

Hydrogen is a chemical element (atomic number 1). It's the most abundant element in the universe, comprising over 90% of all matter. In its molecular state, it's a colorless, odorless gas. It combines readily with oxygen and most other elements, but usually requires a heat source in order to form chemical compounds.
Hydrogen is a component of many organic molecules, most importantly water, but also fat and glucose.
Hydrogen at Wikipedia
Category:Chemistry