Question

Which off the following will be effective for coagulation of as2s3 sol?

Answer 1

As As2S3 is a negatively charged Sol, coagulation will be effective if a positively charged Sol. An example of such Sol is AlCl3 that gives Al3+

Answer 2

Coagulation is the process of conversion of colloidal to precipitate. It can be done with the help of addition of certain chemical compounds which can neutralize the charges of solution and therefore they coagulate.  

Here the solution of $\mathrm{As}_{2} \mathrm{S}_{3}$ has some negatively charge. Hence to coagulate it we need some compound with positive charge.

Therefore compound with more positive charge will be efficient for it. Hence $\bold{\mathrm{AlCl}_{3}}$ can be used as it gives $\mathrm{Al}^{+3}$ ions.