Please give answer to 83rd question with explanation

Dear Student,
1. BC represents a change in phase of the substance.
We can say this because, during a phase change there is no rise in Temperature (As seen in the graph, the temperature remains constant at 60°C). All of the energy is used up in changing the substance from molten to solid state, hence no rise in Temperature during phase change. The substance in molten state solifies, therefore solidification takes place.
2. The lab temperature is 30°C. We can say this because there is no further change of state on decreasing the temperature. And, that the graph has been plotted only until point D.
3. The temperature of the substance after 6 mins is 40°C. If we extrapolate the graph upwards, we find that at 6 mins, the temperature is 40°C.
4. BC represents Solidification. As the substance is initially in the molten state(liquid state), during BC there is phase change( as represented by the constant temperature) and the substance has now changed to solid phase.
Regards
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