(b)
$CaCO_{3} + 2HCl \longrightarrow CaCl_{2} + CO_{2} + H_{2}O$
100 g 73 g 44g
100 mL of 20% $HCl$ = 20 g =$HCl$
In this case, $CaCO_{3}$ is the limiting reactant.
$\because$ 100 g of $CaCO_{3}$ gives $CO_{2} = 44$ g
$\therefore$ 20 g $CaSO_{3}$ will give $CO_{2} = \frac{44 \times 20}{100} = 8.80\ g$