To coagulate gelatin sol, which of the following is most effective ?

A certain sol undergoes anaphoresis under the influence of an electric field. Which of the following is highly effective in the coagulation of this sol-

For coagulation of arsenious sulphide sol, which one of the following salt solution will be most effective ?

For coagulation of arsenious sulphide sol, which one of the following salt solution will be most effective ?

Arsenic (III) sulphide forms a sol with a negative charge which of the following ionic substances should be most effective in coagulating the sol