The heating curve of an ice-water mixture that is slowly heated to 125? C contains three sloped and two level portions. What do the two level portions in the graph represent?

A) heating

B) deposition

C) sublimation

D) phase changes

I believe the answer is D. phase changes. The two level portions represents change of state that does not involve change in temperature (at a constant temperature). The first level represents a change of solid to liquid; p where the ice melts and becomes water by gaining the latent heat of fusion, while the other level represents a change of state from liquid to gas; the water changes to steam (water vapor) by gaining the latent heat of vaporization.