For the coagulation of 500 mL of arsenious sulphide sol, 2 ml of 1M NaCl is required. What i's the flocculation value of NaCl?

$2\mathrm{mL}\text{ of }1\mathrm{MNaCl}\text{ contains }\mathrm{NaCl}=\frac{2}{1000}=2\mathrm{mmol}$

Thus 500 mL of AsrS₃ sol require NaCl for complete coagulation = 2 m mol
Hence 1 L, i.e., 1000 mL of the sol require NaCl for complete
coagulation = 4 m mol
Therefore, flocculation value of NaCl = 4.