Which of the following metals reacts violently with cold water?

Potassium

The correct answer is option 4. Potassium.

The metal that reacts violently with cold water is Potassium.

Potassium is an alkali metal that reacts vigorously with cold water, producing hydrogen gas and forming potassium hydroxide. This reaction is exothermic and can result in the rapid evolution of heat and the production of flames, making it appear as if the metal is reacting violently with the water.