Concept:The percentage composition by mass calculates what fraction of a compound's total molar mass is contributed by each specific element.
Formula:$$ \% \text{ Element} = \left( \frac{\text{Total mass of element in formula}}{\text{Molar mass of compound}} \right) \times 100 $$
Solution:- Calculate total molar mass of \( \text{CO}_2 \): \( 12 + (2 \times 16) = 12 + 32 = 44 \text{ g/mol} \).
- Calculate percentage of Carbon: \( (12 / 44) \times 100 \approx 27.27\% \).
- Calculate percentage of Oxygen: \( (32 / 44) \times 100 \approx 72.72\% \).
- Therefore, the composition is strictly 27.27% Carbon and 72.72% Oxygen.
Why other options are incorrect:- Options A, B, D: These percentages are entirely fabricated and do not reflect the 12:44 and 32:44 mass ratios dictated by the chemical formula.
Quality & Fidelity Assurance:
Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.