What type of mixture exists between the solidus line and the solvus line in a thermal equilibrium diagram?

The area between the solidus line and the solvus line on a thermal equilibrium diagram represents a solid solution. In materials science, particularly in phase diagrams, the solidus line indicates the temperature below which a material is entirely solid, while the solvus line denotes the boundary between a single-phase solid solution and a mixed solid phase.

In this region, both the constituents of the alloy or mixture are present in the solid state, but they are not entirely in a pure form. Instead, they form a single-phase solid solution where the solute is dissolved at the atomic or molecular level within the solvent's crystal lattice. This atomic mixing leads to changes in the properties of the material, such as increased strength or altered melting points, depending on the specific elements involved.

This understanding of solid solutions is crucial for engineering applications, particularly in metallurgy, where manipulating the properties of metals through alloying is often necessary. The other choices do not accurately depict the characteristics of the phase present in this specific region of the thermal equilibrium diagram.