Identify the most reactive and least reactive metal among the following: Al, K, Ca, Au.

Step 1: Reactivity of metals

• Reactivity of the metals means how that metal reacts with other substances.
• In the reactivity series, metals are arranged in decreasing order of reactivity. It is also called an activity series.

Step 2: Most reactive and least reactive:

• Potassium (K) is the most reactive metal because it is the most electropositive and its ionization enthalpy of Potassium is minimum.
• So we can easily remove an electron from the potassium (K).
• Gold is unreactive because the nucleus of the gold is heavy such that the electrons must travel at the speed of light. The 6s electrons in the gold are less accessible for bonding and their energy is dissimilar to many reactants.

Therefore, gold (Au) is the least reactive metal and potassium (K) is the most reactive metal.