Which of the following is an example of solid-solid colloid?

Colloidal solutions (or colloids) are those in which the size of particles is not visible to naked eyes but they can scatter the beam of light.

Colloids are classified on the basis of the physical states of the dispersed phase and the dispersing medium.

When the dispersed phase is solid and the dispersing medium is also solid, then such colloid is referred to as solid sol.

Examples of solid sol are coloured gemstone and milky glass.