Identifying the element with highest mass percentage via molar mass calculations

Steps:

• Compute molar mass of Cu(NO₃)₂: 63.5 (Cu) + 28 (2N) + 96 (6O) = 187.5 g/mol; %O = (96/187.5)×100 ≈ 51% (highest).
• Compute molar mass of ZnSO₄: 65 (Zn) + 32 (S) + 64 (4O) = 161 g/mol; %Zn = (65/161)×100 ≈ 40% (highest).
• Compute molar mass of Na₂S₂O₃: 46 (2Na) + 64 (2S) + 48 (3O) = 158 g/mol; %S = (64/158)×100 ≈ 41% (highest).

Why D is correct:

• Mass percentage is (element mass / compound molar mass) × 100; D matches the highest for each: O in Cu(NO₃)₂, Zn in ZnSO₄, S in Na₂S₂O₃.

Why the others are wrong:

• A: Cu (34%) < O in Cu(NO₃)₂; O not highest in ZnSO₄ (Zn) or Na₂S₂O₃ (S).
• B: S (20%) < Zn in ZnSO₄; S (41%) highest in Na₂S₂O₃ but row mismatches second compound.
• C: S (20%) < Zn in ZnSO₄; Na (29%) < S in Na₂S₂O₃.

Final answer: D