Trends in Group 1 Metal Properties

Steps:

• Recall that Group 1 metals are alkali metals, with properties changing down the group from lithium to potassium.
• Note melting points: Li (180°C), Na (98°C), K (63°C), showing a decrease due to weaker metallic bonding from larger atoms.
• Observe reactivity with water: Li reacts steadily, Na fizzes vigorously, K ignites explosively, indicating increasing vigor.
• Combine trends: decreasing melting points and increasing reactivity confirm option B.

Why B is correct:

• Down the group, atomic size increases, weakening metallic bonds (fewer delocalized electrons per atom) for lower melting points, while easier electron loss boosts reactivity per the reactivity series.

Why the others are wrong:

• A: Reaction becomes more vigorous, not less.
• C: Melting points decrease, not increase.
• D: Both melting points decrease and reaction increases, not the reverse.

Final answer: B