Which of the following is a natural colloid?

Which principle is applicable in the purification of water using alum?

Which of the following electrolytes will have the maximum flocculation value for $Fe(OH)_3$ sol?

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.

Dispersed colloidal iron $(III)$ hydroxide and colloidal gold are positively and negatively charged,respectively. Which of the following statements is $NOT$ correct?

Which of the following colloidal solutions cannot be prepared by Bredig's arc method?