Answer
a. Mass/volume percent(m/v) = $30 \%$ (m/v) $Na_2SO_4$ solution
b. Mass/volume percent(m/v) = $11 \%$ (m/v) $sucrose$ solution
Work Step by Step
a.
1. Write the expression for the mass/volume percent:
$$Mass/volume \space percent(m/v) = \frac{grams \space of \space solute}{mL \space of \space solution} \times 100\%$$
$$Mass/volume \space percent(m/v) = \frac{ 75 \space g \space Na_2SO_4 }{ 250 \space mL \space Na_2SO_4 \space solution} \times 100\%$$
Mass/volume percent(m/v) = $30 \%$ (m/v) $Na_2SO_4$ solution
b.
1. Write the expression for the mass/volume percent:
$$Mass/volume \space percent(m/v) = \frac{grams \space of \space solute}{mL \space of \space solution} \times 100\%$$
$$Mass/volume \space percent(m/v) = \frac{ 39 \space g \space sucrose }{ 355 \space mL \space carbonated \space drink} \times 100\%$$
Mass/volume percent(m/v) = $11 \%$ (m/v) $sucrose$ solution