According to principle of calorimetry, heat gained = heat lost Heat is lost by steam in two stages (i) Change of state from steam at 100°C to water at 100°C is m×540 (ii) To change water at 100°C to water at 80°C is m×1×(100−80), where m is the mass of the steam condensed. Total heat lost by steam is m×540+m×20=m(540+20)=560m Heat gained by calorimeter and its contents is (1.1+0.2)×(80−15)=1.12×65cal ⇒ 560m=1.12×65 ⇒m=1.12×65.560=0.130kg