**Question:**

Arun has prepared $0301 \%$ (by mass) solution of sodium chloride in water. Which of the following correctly represents the composition of the solution?

(a) $1.00 \mathrm{~g}$ of $\mathrm{NaCl}+100 \mathrm{~g}$ of water

(b) $0.11 \mathrm{~g}$ of $\mathrm{NaCl}+100 \mathrm{~g}$ of water

(c) $0.01 \mathrm{~g}$ of $\mathrm{NaCl}+99.99 \mathrm{~g}$ of water

(d) $0.10 \mathrm{~g}$ of $\mathrm{NaCl}+99.90 \mathrm{~g}$ of water.

**Solution:**

By definition $0.01 \%$ (by mass) solution means that $0.01 \mathrm{~g}$ of sodium chloride is dissolved in $0.99 \mathrm{~g}$ (by mass) of water. Therefore (c) represents the correct composition of the solution. This can be further verified as follows:

Mass percent $=\frac{\text { Mass of sodium chloride }}{\text { Mass of solution }} \times 100$

$=\frac{(0.01 g)}{(0.99+0.01)} \times 100=0.01 \%$