Lithium, sodium, and potassium are examples of _________.

• A. Noble gases
• B. Halogens
• C. Transition metals
• D. Alkali metals

Answer: (D)

These elements are alkali metals, occupying Group 1 of the periodic table. They all have a single valence electron, which they readily lose to form a +1 ion. That loose hold on the outer electron makes them extremely reactive, especially with water, where they fizz, heat up, and release hydrogen gas while forming a basic metal hydroxide. Lithium, sodium, and potassium are classic examples of this group, and they’re typically stored under oil to keep them from reacting with moisture in the air. They’re also soft and have low densities, with reactivity that increases down the group (potassium reacts more vigorously than lithium). They’re not noble gases, halogens, or transition metals, which have different properties and lie in different parts of the periodic table.