Hydrogen is a colourless, odourless, lighter than air gas.
Molecular Hydrogen (H2) H2 is a gas which forms when two hydrogen atoms bond together and become a hydrogen molecule. It consists of two protons and two electrons and is the most common form of Hydrogen because it is stable with a neutral charge. Hydrogen (H2) as a gas poses a number of hazards to human health from potential explosion to asphyxiant in its pure form. It will burn in concentrations a low as 4% in air. Wet cell batteries are a particular hazard as gaseous hydrogen forms on the cathode and then escapes to atmosphere potentially creating a risk of detonation.