What is the percent by mass of carbon in glucose? %

Glucose has the formula C₆H₁₂O₆. Its six carbon atoms contribute about 6 × 12 = 72 g/mol, while the whole molecule has a molar mass of about 180 g/mol. The carbon mass percentage is (72 ÷ 180) × 100 = 40.0%, so the correct choice is 40.0.

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