Why do we add alum to purify water?

The charge on $As_2S_3$ sol is due to the adsorbed

Ferric chloride is applied to stop bleeding from a cut because:

Identify the incorrect statement.

Given below are two statements:
Statement $I:$ In the coagulation of a negative sol,the flocculating power of the three given ions is in the order - $Al^{3+} > Ba^{2+} > Na^{+}$
Statement $II:$ In the coagulation of a positive sol,the flocculating power of the three given salts is in the order - $NaCl > Na_{2}SO_{4} > Na_{3}PO_{4}$
In the light of the above statements,choose the most appropriate answer from the options given below:

Which of the following information is incorrect?