The volume in litres of  $C{O}_2$ liberated at STP, when 10g of 90% pure limestone is heated completely is

10 gms of 90% pure lime stones means  $\frac{90}{100}\times 1.0$

= 9 gms of pure  $CaC{O}_3$

$CaC{O}_3\to CaO+C{O}_2$

100 gms       22.4 lit at STP

9 gms           X lit at STP

$\therefore$ volume of $C{O}_2=\frac{9\times 22.4}{100}$ lit at STP

= 2.016 lit at STP