10 grams of limestone on calcination liberates 1.68 lit  of CO2 at STP. Percentage purity of limestone is

CaCO3S →   CaOs  +  CO2g100 g                                                     22.4 lit10 g                                                        2.24 lit    10 grams of 100% pure limestone liberates 2.24 lit CO2 of  at STP10 grams of “X%” pure limestone liberates 1.68 lit of CO2  at STPPercentage purity  (X)  = 1.682.24  ×  100                                                = 75 %