Rubidium’s reactivity compared to lithium, sodium and potassium.

• A. Less reactive than lithium, sodium and potassium.
• B. More reactive than lithium, sodium and potassium.
• C. As reactive as lithium, sodium and potassium.
• D. Only more reactive than potassium.

Answer: (C)

Reactivity among alkali metals increases as you move down the group. As you go from lithium to sodium to potassium to rubidium, the outer electron is held less tightly because the atom is larger and there is more shielding. That makes it easier to lose that outer electron and react, especially with water.

Rubidium sits below potassium, so it has a lower ionization energy and a larger atomic size than lithium, sodium, and potassium. This means it will lose its outer electron more readily than those elements, making it more reactive than all three. So the correct way to describe rubidium’s reactivity is that it is more reactive than lithium, sodium and potassium.