Question

During which period is the substance changing state?

A. During the time labeled C, when the temperature increases
sharply.
B. During the time labeled E, when the temperature increases for a
third time.
C. During the time labeled A, when the temperature first starts to
increase.
D. During the time labeled D, when the temperature stays the same.
SIDANT

Answer 1

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

Step-by-step 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.