Hydrogen is a gas. its atomic number is 1 and its the first element on the periodic table. Hydrogen only makes up 1% of the world but it is the most commonly found element in the universe! Did you know that the stars and the sun are mainly made up of hydrogen?Cool right, but it gets even better, because hydrogen is such a light wieght gas, it's the reason there is zero gravity in outer space. So you see, hydrogen is an amazing element!