(1) water molecule(2) It works by affecting a molecule called nitric oxide, which expands blood vessels.(3) In the water molecule there are three atoms: two of hydrogen and one of oxygen.(4) At the root of sunburn are damaging molecules , free radicals that increase when the skin gets too much sun.(5) The reactant ions have enough energy to ionise the molecules of interest but not enough to break them up.(6) This electricity splits the water molecules in an electrolyte, producing hydrogen.