Correct Answer - A
When heat is supplied the temperature of ice increase from `- 10^(@)C` to `0^(2)C` . It is represented by a straight line inclined to heat axis. At `0^(@)C` the heat is used in converting ice into water at `0^(@)C`. This stage is represented by horizontal straight portion. After that represented by horizontal straight portion. After that temperature of water rises from `0^(@)C` to `100 .^(@)C`. It is represented by a straight line inclined to heat axis. At `100^(@)C`, the heat is used in converting water into steam. The graph is represented by horizontal straight line. Thus option (a) is correct.