Which metal is the most reactive in the standard reactivity series among the following?

• A. Gold
• B. Potassium
• C. Silver
• D. Copper

Answer: (B)

Reactivity series tells us how readily metals lose electrons to form positive ions; the easier it is to remove electrons, the more reactive the metal is. Potassium has a very low first ionization energy and a strongly negative tendency in reduction potentials, so it is oxidized far more readily than the others. This shows up in real life as potassium reacting violently with water to produce KOH and H2, a hallmark of high reactivity. The other metals here—for example, gold—are very resistant to oxidation and hardly react under ordinary conditions; silver is relatively inert and only slowly tarnishes, while copper oxidizes slowly to form a patina. So potassium stands out as the most reactive among these metals.