# Calculate the mass of $CaO$ that shall be obtained by heating 20kg of 80% pure lime-stone $(CaCO_3)$

$(a)\;8\qquad(b)\;5\qquad(c)\;9\qquad(d)\;10$

$CaCO_3\rightarrow CaO+CO_2$
$CaCO_3\Rightarrow 100kg$
$CaO\Rightarrow 56kg$
Pure lime stone 20kg of 80%$=\large\frac{20\times 80}{100}$
$\Rightarrow 16kg$
$100kg \;CaCO_3$ gives =$56kg\;CaO$
$16kg\;CaCO_3$ give =$\large\frac{56\times 16}{100}$
$\Rightarrow 8.96$
$\approx 9kgCaCO$
Hence (c) is the correct answer.