BITSAT 2018 Slot 2 Solved Paper

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