Answer
The temperature of the sample increases to 0$^{\circ}$C and then remains constant. It then melts and the temperature increases untill 25$^{\circ}$C and remains constant.
Work Step by Step
The temperature of the sample is colder than the room temperature so the sample temperature increases to 0$^{\circ}$C and then remains constant. It then melts and the temperature increases till 25$^{\circ}$C and remains constant because that is the room temperature.