Into how many parts are colloidal sols divided according to the nature of interaction between the dispersed phase and the dispersion medium?

State the $Hardy-Schulze$ rule.

Which of the following is an emulsifier?

$20 \ mL$ of $0.5 \ M \ NaCl$ is required to coagulate $200 \ mL$ of $As_2S_3$ sol in $2$ hours. The coagulating value of $NaCl$ is $...........$.

When a few drops of dilute $HCl$ are added to a freshly prepared precipitate of ferric hydroxide,a reddish-brown colloidal solution is obtained. This phenomenon is known as .......

The impurities present in rain water possess $.....$ charge.