Which of the following sols is negatively charged?

Arsenious sulphide sol has a negative charge, therefore positive ions can cause it to coagulate. The ability of the flocculating ion to produce precipitation increases with valency. ${\mathrm{AlCl}}_3$ has a positive cation with the greatest valency of +3 in all of the mentioned compounds. It has the most precipitating power as a result.
Negatively charged sols are either metal sols or metal sulphide sols, whereas positively charged sols are typically metal hydroxides. As ${\mathrm{As}}_2{\mathrm{S}}_3$ is a metal sulphide, it has a negative charge.