The graph provided shows the change in temperature with time when a solid is melted and then allowed to cool and solidify again. There is a portion of the curve that is practically horizontal, indicating that the temperature remains constant during this period.

Option 1 states that the practically horizontal part of the curve is due to latent heat given away by the liquid. Latent heat is the heat energy absorbed or released during a phase change, such as when a solid changes to a liquid or a liquid changes to a solid. In this case, when the solid is melted, it absorbs latent heat from its surroundings, and when the liquid is solidifying, it releases latent heat to its surroundings. This release of latent heat keeps the temperature constant during this phase change, which explains the horizontal portion of the curve.

Option 2 suggests that the horizontal portion is due to specific heat given away by the liquid. Specific heat is the amount of heat energy required to raise the temperature of a substance by a certain amount. However, the specific heat of the substance does not affect the change in temperature during a phase change, so this option is not applicable.

Option 3 states that the thermal capacity changes with time, keeping the temperature constant. However, the thermal capacity of a substance does not change with time