Step 1: Understanding the Concept
A colloid is named by the states of its dispersed phase and dispersion medium.
Step 2: Match
Solid in liquid is a sol, liquid in liquid is an emulsion, gas in liquid is a foam, and solid or liquid in gas is an aerosol.
Step 3: Result
Solid dispersed phase with liquid medium is a sol, for example paint or gold sol.
Final Answer:
A colloid of a solid in a liquid is a sol.
\[ \boxed{\text{(C) }\text{Sol}} \]