In an experiment, addition of `4.0mL` of `0.005MBaCl_(2)` to `16.0mL` of arsenious sulphide sol just cause the complete coagulation in `2h` . The flocculating value of the effective ion is:
A. `Cl^(Θ),1.0`
B. `Cl^(Θ),2.0`
C. `Ba^(2+),1.0`
D. `Ba^(2+),0.5`