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# A solution of ethanol in water is 10% by volume. If the solution and pure ethanol have densities of 0.9866 g/cc and 0.785 g/cc respectively, find the per cent by weight of ethanol.

Volume of ethanol = 10 ml
Volume of solution = 100 ml
Weight percentage = ?
We know,Weight percentage(w/w)=$\large\frac{\text{Weight of solute}}{\text{Weight of solution}}$$\times 100 Weight of ethanol = Volume \times Density = 10 \times 0.785 = 7.85 g Weight of solution = 100 \times 0.9866 = 98.66 g Substituting the above values in (1), we get \therefore Weight percentage =\large\frac{7.85}{98.66}$$\times 100=7.95\%$
Hence (A) is the correct answer.