Which trend describes the reactivity of Group 1 elements as you go down the group?

• A. Increases down the group
• B. Decreases down the group
• C. Remains the same
• D. First increases then decreases

Answer: (A)

As you go down Group 1, reactivity increases. The outer electron that these metals must lose to react is held less tightly the further it is from the nucleus. When you move down the group, the atomic radius gets larger and there’s more shielding by inner electrons, so the attraction between the nucleus and the outer electron weakens. That makes losing that outer electron easier, which means the metals react more readily.

In practice, this shows up in reactions with water: lithium reacts slowly, sodium more vigorously, and potassium (and the heavier alkali metals) react very readily, sometimes with flames. They all form hydroxides and hydrogen gas, but the rate of reaction climbs as you go down the group because losing the outer electron becomes easier.

So the trend is an increasing reactivity down the group, driven by decreasing ionization energy due to greater atomic size and shielding.