A solid is melted and allowed to cool and solidify again. The temperat

A solid is melted and allowed to cool and solidify again. The temperature is measured at equal intervals of time. The graph below shows the change of temperature with time.
[Graph image is part of the question context]
The part of the curve that is practically horizontal is due to

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latent heat given away by the liquid

specific heat given away by the liquid

thermal capacity changes with time keeping temperature constant

change in density during transformation

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This question was previously asked in

UPSC NDA-1 – 2015

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The horizontal part of the cooling curve represents a phase transition. As the liquid cools and reaches its freezing point, it starts to solidify. During the solidification process, the temperature remains constant because the substance is releasing latent heat of fusion (or solidification). This released latent heat compensates for the heat being lost to the surroundings, preventing the temperature from dropping until all the liquid has solidified.

During a phase change (like melting or freezing), the temperature of a pure substance remains constant as latent heat is absorbed or released.

Latent heat is the heat energy absorbed or released by a substance during a phase change at constant temperature. Specific heat is the heat required to raise the temperature of a unit mass of a substance by one degree within a single phase.

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