Concept:Metals higher in the reactivity series are more reactive because they lose electrons more easily.Explanation:Increasing reactivity means arranging metals from the least reactive to the most reactive.The order of the given metals from least reactive to most reactive is:Au<Cu<Sn<Fe<CaGold is the least reactive among them, followed by copper, tin, iron, and calcium.Calcium is highly reactive and reacts readily with water and acids.Answer:Option A: Au<Cu<Sn<Fe<Ca