Which of the following will have the highest coagulating power for $As_2S_3$ colloid?

The correct option among the following is:

On adding a few drops of dilute $HCl$ or $FeCl_3$ to freshly precipitated ferric hydroxide,a red-coloured colloidal solution is obtained. This phenomenon is called:

Choose the correct reason$(s)$ for the stability of the lyophobic colloidal particles.
$(A)$ Preferential adsorption of ions on their surface from the solution.
$(B)$ Preferential adsorption of solvent on their surface from the solution.
$(C)$ Attraction between different particles having opposite charges on their surface.
$(D)$ Potential difference between the fixed layer and the diffused layer of opposite charges around the colloidal particles.

Tyndall effect is more effectively shown by:

Photographic plates are prepared by coating an emulsion of which of the following in gelatin?