20 ml of $C{O}_2$ is passed over red hot coke. The volume of CO evolved is:

$C+C{O}_2\to 2CO$

The correct option is B 40
$C{O}_2+C\to 2CO$

$22.4$ ltr of $C{O}_2$ gives $2\times 22.4$ of $CO$

$1$ ltr of $C{O}_2$ gives $\frac{2\times 22.4}{22.4}$ of $CO$

$20\times {10}^{-3}$ ltr of $C{O}_2$ gives $\frac{2\times 22.4\times 20\times {10}^{-3}}{22.4}$ of $CO$

$=0.04$

$=40$ cc of $CO$

Hence, the correct answer is B.