Gold number is minimum in the case of

In each of four separate beakers $(I, II, III, IV)$,$X \ mL$ of $y \ M \ Fe_2O_3 \cdot xH_2O$ colloidal solution is present. Equal volume and equal concentration of $KCl, K_4[Fe(CN)_6], K_3PO_4$ and $K_2SO_4$ were added into $I, II, III$ and $IV$ respectively. The efficiency of precipitation in these beakers follows the order:

Provide information about the charge on colloidal particles.

The function of gum-arabic in the preparation of Indian ink is:

In the precipitation of soap,which can be used instead of $NaCl$?

Which of the following is not correct?