In a phase diagram, the line separating the solid and liquid phases represents the melting point of a substance at a given pressure. True or False?

True. In a phase diagram the boundary that runs between the solid and liquid regions marks the temperatures at which the substance changes from solid to liquid or vice versa, depending on the pressure. This line is called the melting curve because it shows the melting point for each pressure value. For example, at atmospheric pressure water melts at 0 °C, so the line passes through that point. Thus the line indeed represents the melting point as a function of pressure.