Which one among the following is the most reactive metal?

The reactivity of a metal is determined by its ability to lose electrons and form positive ions. According to the reactivity series, metals are arranged in descending order of their chemical reactivity. Among the options provided, the order of reactivity from highest to lowest is:

Potassium (K) > Sodium (Na) > Calcium (Ca) > Magnesium (Mg)

Potassium (K) is an alkali metal (Group 1) and is extremely reactive because it has a large atomic radius and low ionization enthalpy, allowing it to lose its single valence electron very easily. It reacts vigorously even with cold water. While Sodium (Na) is also highly reactive, Potassium is more reactive due to its position further down in Group 1. Calcium and Magnesium are Group 2 alkaline earth metals and are generally less reactive than Group 1 metals.