UPSC NDA 2 2017 General Ability Solved Paper

Concept:Compare mass percentages of elements in $\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_4$ using atomic masses.Explanation:Atomic masses: $\mathrm{C}=12$, $\mathrm{H}=1$, $\mathrm{O}=16$ (in u).Molar mass = $6\times12 + 12\times1 + 4\times16 = 72 + 12 + 64 = 148$ g/mol.Mass percent of $\mathrm{C}$ = $\frac{72}{148}\times100\%$.Mass percent of $\mathrm{H}$ = $\frac{12}{148}\times100\%$.Mass percent of $\mathrm{O}$ = $\frac{64}{148}\times100\%$.Ratio of mass percent of $\mathrm{C}$ to $\mathrm{H}$ = $\frac{\frac{72}{148}}{\frac{12}{148}} = \frac{72}{12} = 6$.Thus, mass percent of carbon is 6 times that of hydrogen.Option A is incorrect: 22 atoms per molecule, not per mole (per mole means Avogadro's number).Option B and D give wrong comparisons.Answer:Option C: six times the mass percent of C as compared to the mass percent of H.