Correct option is (1)
First heat is supplied to raise temperature of ice from –10°C to 0°C. Now heat supplied is latent heat of fusion of ice. During this stage temperature remains constant at 0°C. Now heat supplied raises temperature of water formed from 0°C to 100°C. Then heat supplied is latent heat of vaporisation. There is no change in temperature due to heat given. These features are correctly represented by curve (1).