Assessing student claims on metal properties

Steps:

• Examine Student X's claim: The reactivity series places Group I metals (K, Na) at the top, above hydrogen, as they displace H from acids; transition metals like Fe, Zn are mostly above H, but X wrongly places Group I below H.
• Verify Student Y's claim: Group I metals have low densities (e.g., Na at 0.97 g/cm³ due to large atomic size and low mass); transition metals have high densities (e.g., Fe at 7.87 g/cm³ from compact d-block structure).
• Compare to options: X is incorrect on reactivity order; Y is accurate on densities.
• Conclude only Y is right, selecting C.

Why C is correct:

• Y matches periodic trends: Atomic radii increase down Group I, lowering density, while transition metals' d-electrons enable denser packing.

Why the others are wrong:

• A: X's reactivity claim inverts the series, falsifying both correct.
• B: X misplaces Group I below H, opposite to their high reactivity.
• D: Ignores Y's valid density comparison.

Final answer: C