Muddy water can be purified through coagulation using

Colloidal solution of arsenious sulphide can be prepared by:

Identify the correct statements from the following:
$(i)$ $A$ closed vessel containing $90 \%$ $CO_2$ and $10 \%$ $O_2$ is an aerosol.
$(ii)$ Milk is an emulsion.
$(iii)$ Smoke is an aerosol.
$(iv)$ Peptisation is a method of purification of colloidal solution.
$(v)$ Ultrafiltration is a method of purification of colloidal solution.

Which of the following colloidal systems represents a sol?

The coagulation of $10 \, mL$ of gold sol is prevented by the addition of $0.025 \, g$ of starch to it before adding $1 \, mL$ of $10 \% \, NaCl$ solution. The gold number of starch is .............

On addition of $1 \, mL$ solution of $10\% \, NaCl$ to $10 \, mL$ gold sol in the presence of $0.25 \, g$ of starch,the coagulation is just prevented. What is the gold number of starch?