A scientist heats an unknown substance in a closed system. The graph shows the change in temperature over time.

C

Explanation:

When a substance is changing state, the heat supplied does not result in a rise in temperature. This is why, the heat supplied during change of state is referred to as 'latent heat'.

Latent heat is a heat that causes a change of state without a corresponding rise in temperature. During this time, the intermolecular bonds in the substance are broken.

Change of state will occur as regions in which there is no change in temperature with time such as point D on the graph.

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