Which metal is more reactive, Potassium or Calcium?

• A. Potassium
• B. Calcium
• C. Both are equally reactive
• D. Neither reacts with acids

Answer: (A)

Reactivity of metals is all about how easily they lose electrons. Potassium, an alkali metal with one valence electron, loses that electron far more readily than calcium, which must lose two electrons. This easier loss comes from a lower first ionization energy and a larger atomic size, both of which make the outer electron easier to remove. Because losing electrons drives the reactions with water or acids, potassium reacts very vigorously, while calcium, needing more energy to remove a second electron, reacts less vigorously. So potassium is more reactive overall. (D is not true—both metals can react with acids, and calcium isn’t equally reactive to potassium.)