Most Abundant Element by Mass Percentage

Steps:

• Compute molar mass: CaCO₃ (100 g/mol), K₂SO₄ (174 g/mol), Zn(NO₃)₂ (189 g/mol).
• Calculate mass percentages: CaCO₃ (O: 48%, Ca: 40%); K₂SO₄ (K: 45%, O: 37%); Zn(NO₃)₂ (O: 51%, Zn: 34%).
• Identify highest: oxygen in CaCO₃, potassium in K₂SO₄, oxygen in Zn(NO₃)₂.

Why D is correct:

• Option D lists oxygen (highest in CaCO₃ and Zn(NO₃)₂) and potassium (highest in K₂SO₄), based on mass percentage formula: (element mass / compound mass) × 100.

Why the others are wrong:

• A: Blank; provides no elements.
• B: Lists calcium (not highest in CaCO₃) and zinc (not highest in Zn(NO₃)₂).
• C: Lists oxygen for K₂SO₄ (potassium is higher).

Final answer: D