Answer
(a) $17.1 \% $
(b) $13.9 \%$
(c) $13.7\%$
Work Step by Step
(a)
$$Percent \space by \space volume = \frac{12.8 \space mL}{75.0 \space mL} \times 100\%= 17.1 \% $$
(b)
Mass of solute : $12.8 \space mL \times \frac{0.803 \space g}{1 \space mL} = 10.3 \space g$
Mass of solution: $75.0 \space mL \times \frac{0.988 \space g}{1 \space mL} = 74.1 \space g$
$$Percent \space by \space mass = \frac{10.3 \space g}{74.1 \space g} \times 100\% = 13.9 \%$$
(c) $$Percent(mass/volume) = \frac{10.3 \space g}{75.0 \space mL} \times 100\% = 13.7\%$$
