Who introduced the concept of $Gold \ Number$?

Give information about colloids. Explain the classification of colloids.

Suspensions are

Flocculation value of $BaCl_2$ is much less than that of $KCl$ for sol $A$ and flocculation value of $Na_2SO_4$ is much less than that of $NaBr$ for sol $B.$ The correct statement among the following is

For the coagulation of a negatively charged clay sol in water,the minimum amount of which of the following is required?

Fog is an example of which type of colloid?