When 50 g of calcium carbonate is heated, 22g of ${\text{CO}}_2$ escapes out. What is the amount of residue left

The decomposition reaction of Calcium Carbonate on heating is

${\text{CaCO}}_{\text{3}}\left(\text{s}\right)\stackrel{\Delta }{\to }\text{CaO(s)}+{\text{CO}}_2\left(g\right)$

$\mathbf{100}{\mathbf{\text{g\hspace{0.17em}of\hspace{0.17em}CaCO}}}_{\mathbf{\text{3}}}\mathbf{\to }\mathbf{5}\mathbf{\text{6g\hspace{0.17em}of\hspace{0.17em}CaO}}\mathbf{+}{\mathbf{\text{44g\hspace{0.17em}of\hspace{0.17em}CO}}}_{\mathbf{\text{2}}}$

$50{\text{\hspace{0.17em}g of CaCO}}_3\to x\text{\hspace{0.17em}of\hspace{0.17em}CaO}$
$x=\frac{50\times 56}{100}=28\text{\hspace{0.17em}g}$.

Therefore, the amount of residue (CaO) left over is 28g.