Which of the following statements best describes a solid solution?

A solid solution is a homogeneous mixture of two or more different types of atoms within a solid crystalline lattice. In the context of metals, solid solutions typically occur when one type of metal atom can substitute or incorporate into the crystal structure of another metal, forming a single-phase material where the different metal atoms are uniformly distributed.

The choice indicating that a solid solution involves a mixture of different metal types accurately reflects the essential characteristic of solid solutions. In this case, the different metal atoms can occupy the same lattice sites or be interspersed within the crystal structure, which enhances the material's properties, such as strength or electrical conductivity.

The other options describe scenarios that do not align with the definition of a solid solution. Gas composed of metal atoms is not applicable since a solid solution implies a solid state. Solely non-metal atoms do not describe a solid solution, as these typically involve metallic elements that can form alloys. Finally, the statement about the inability to substitute atoms in the lattice is contrary to the fundamental nature of solid solutions, where substitution of atoms is a key feature.