Which instrument is used for the determination of particle size?

Assertion : Colloidal solutions are stable but colloidal particles do not settle down.
Reason : Brownian movement counters the force of gravity actively on colloidal particles.

The most suitable electrolyte for the coagulation of arsenic sulphide sol will be

$A$ liquid scatters light and leaves no residue when passed through filter paper. This liquid can be described as..........

Zeta potential is

Gold sol is not a