(b)
Given, moles of $Ba(OH)_{2}$=0.205
$Ba(OH)_{2} + CO_{2} \rightarrow BaCO_{3} + H_{2}O$
$\therefore$ 0.205 moles of $Ba(OH)_{2} \equiv$0.205 moles of $BaCO_{3}$
$\therefore$ Mass of $BaCO_{3}$=moles of $BaCO_{3} \times$ molecules mass of $BaCO_{3}$
$= 0.205 \times 197.3$
$= 40.5$ g