The coagulating power of electrolytes having ions `Na^(+),Al^(3+)` and `Ba^(2+)` for aresenic sulphide sol increases in the order :-

Options

A. `Al^(3+) lt Na^(+) lt Ba^(2+)`
B. `Al^(3+) lt Ba^(2+) lt Na^(+)`
C. `Na^(+) lt Ba^(2+) lt Al^(3+)`
D. `Ba^(2+) lt Na^(+) lt Al^(3+)`

Explanation

`As_2S_3` is a negatively charged sol. Therefore, coagulating power is proportional to the valency of the active (positive) ion (Hardy Schulze rule)
`:. Al^(3+) gt Ba^(2+) gt Na^(+) or Na^(+) lt Ba^(2+) lt Al^(3+)`