When a metal reacts with water, it typically produces hydrogen gas. This reaction is known as a hydrolysis reaction. The reactivity of metals with water varies, with alkali metals (such as sodium and potassium) being the most reactive and noble metals (such as gold and silver) being the least reactive. The general equation for the reaction of a metal with water is:

Metal + Water → Metal Hydroxide + Hydrogen Gas

For example, when sodium reacts with water, it produces sodium hydroxide and hydrogen gas:

2Na + 2H2O → 2NaOH + H2