Earlier the term 'Colloids' was used for a category of substances. However, later, the term colloidal state of matter was preferred. Colloidal dispersions have been classified into different types depending upon the physical state of the dispersed phase and the dispersion medium or the nature of the colloidal particles. They are prepared in the industry or in the laboratory by a number of methods and then purified. Their property has also been studied in detail. Hardy and Schulze made a substantial contribution in studying the coagulation of the colloidds. The protective action of lyophilic colloids was studied by Zsigmondy and he introduced a term, called 'gold number'.

Which of the following will have the maximum flocculation value for arsenic sulphide solution?

NaCl

The correct answer is option 1. NaCl.

To coagulate negative sol of \(As_2​S_3\)​, the coagulation power of different cations decrease in the order \(Al^{3+} > Ba^{2+} > K^+ > Na^+\).

Hence, the flocculation value increases in the order \(Al^{3+} < Ba^{2+} < K^+ < Na^+\)

The flocculating values (in milli moles/litre) of \(Al^{3+} < Ba^{2+} < K^+ < Na^+\) are 0.093, 0.69, 50 and 51 respectively.