1. The first question asks: Which metal is most reactive among Li, Na, K, and Be? 2. Reactivity of metals in the alkali group increases as we move down the group in the periodic table because the outer electron is farther from the nucleus and more easily lost. 3. Li (Lithium), Na (Sodium), and K (Potassium) are alkali metals, while Be (Beryllium) is an alkaline earth metal and less reactive. 4. Among Li, Na, and K, potassium (K) is the most reactive metal because it is the lowest in the group. 5. Therefore, the answer is K. Final answer: K