Which of the following metals reacts with water according to the reactivity series?

Calcium is a metal that reacts readily with water, particularly cold water, to produce calcium hydroxide and hydrogen gas. This reaction demonstrates the typical behavior of alkaline earth metals, such as calcium, which are positioned higher on the reactivity series.

In contrast, iron and zinc can react with water but typically require elevated temperatures or specific conditions to do so. Copper is much lower on the reactivity series and does not react with water at all. The placement of calcium higher in the reactivity series directly indicates its propensity to react with water, making it the correct answer.