Question

During which period is the substance changing state?

Answer 1

Answer:

$\boxed {\boxed {\sf D. \ During \ the \ time \ labeled \ D, \ when \ the \ temperature \ stays \ the \ same}}$

Explanation:

Phase changes have to happen at a specific temperature. During a phase change, the energy is used to make the change happen, instead of raising the temperature.

On a graph, a constant slope, or in this case temperature, is a flat line. On this graph, the flat lines are at B and D.

There is no answer including B, but there is for D.

Choice D: During the time labeled D, when the temperature stays the same is correct.