Which category includes lithium, sodium, and potassium?

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

Answer: (C)

The group is alkali metals. Lithium, sodium, and potassium are all in Group 1, sharing a single valence electron. That makes them highly reactive (they readily lose that electron to form +1 compounds), soft and light, and they’re stored under oil to keep moisture and air away. These properties—especially the one-valence-electron behavior and the high reactivity—define alkali metals.

Noble gases are inert gases, so they don’t fit. Halogens are highly reactive nonmetals that tend to gain electrons, not lose them. Transition metals are in the middle of the periodic table and have variable oxidation states and metallic behavior different from Group 1 elements.