Question

1. the substance is a solid at point _____

f
b
d
a

Explanation:

Step1: Analyze phase - change graph

On a temperature - time graph for a substance, the solid phase is before the melting point.

Step2: Identify solid - phase point

At point A, the substance has not yet started to melt and is in the solid phase. Points B and C are during the melting process (solid - liquid co - existence), point D is after melting (liquid phase), and point F is also in a non - solid phase.

Answer:

A. A