The most reactive metals, such as sodium, will react with cold water to produce hydrogen and the metal hydroxide:
:2 Na (s) + 2 HO (l) →2 NaOH (aq) + H (g)
Metals in the middle of the reactivity series, such as iron, will react with acids such as sulfuric acid (but not water at normal temperatures) to give hydrogen and a metal salt, such as iron(II) sulfate:
:Fe (s) + HSO (l) → FeSO (aq) + H (g)
There is some ambiguity at the borderlines between the groups. Magnesium, aluminium and zinc can react with water, but the reaction is usually very slow unless the metal samples are specially prepared to remove the surface passivation layer of oxide which protects the rest of the metal. Copper and silver will react with nitric acid; but because nitric acid is an oxidizing acid, the oxidizing agent is not the H ion as in normal acids, but the NO ion.