Reactivity and Storage of Alkali Metals

Steps:

• Evaluate A: Group I loses one electron easily, making them more reactive than Group II in the same period.
• Evaluate B: Group I metals react vigorously with air's oxygen and moisture, requiring oil storage.
• Evaluate C: Outer shell electrons remain one down the group; reactivity increases due to larger atomic radius easing electron loss.
• Evaluate D: Melting points decrease from weaker metallic bonds due to larger atoms, not stronger attractions.

Why B is correct:

• Alkali metals tarnish rapidly by reacting with O₂ and H₂O (e.g., 2Na + 2H₂O → 2NaOH + H₂), so oil prevents contact per standard lab safety protocols.

Why the others are wrong:

• A: Group I is more reactive than Group II due to lower ionization energy for one electron.
• C: Outer electrons stay constant at one; reactivity rises from decreasing effective nuclear charge on valence electron.
• D: Larger ions down the group reduce delocalized electron density, weakening metallic bonds and lowering melting points.

Final answer: B