(informal) dihydrogen monoxide (water (H₂O), but not hydrogen peroxide (H₂O₂) or the hydroxyl radical (-OH))

(chemistry) potassium bicarbonate

(inorganic chemistry, chiefly Britain) Alternative spelling of hydrogen sulfide

(inorganic chemistry) The compound sodium hydrogen arsenate.

(chemistry) the hydride of selenium, H₂Se; it is a toxic, inflammable gas, having properties similar to those of hydrogen sulfide

(inorganic chemistry) An inorganic compound with the formula HCl. Forms hydrochloric acid when dissolved in water.

(physics) Any of several series of spectral lines of hydrogen that correspond to quantum transitions between the various allowed energy levels of the hydrogen atom.

(inorganic chemistry, countable) Synonym of bicarbonate / (inorganic chemistry, uncountable) carbonic acid

(physics) all the lines in the emission or absorption spectrum of hydrogen; each one corresponding to an allowed transition between quantum energy levels

A service station for hydrogen vehicles.