For coagulation of 10ml of a positive sol, the volume of 1M each `NaCl, Na_2SO_4, Na_3PO_4` and `Na_4[Fe(CN)_(6)]` required separately are P,Q, R and S ml respectively. Arrange P, Q , R and S in the descending order.

Explanation

For coagulation of a positive sol, negative ions are required. As per Hardy-Schulze rule greater the valence of the flocculating ions, greater is the flocculating power and lesser volume is required.
Thus, the correct order of the volume of solutions is : `P > Q > R > S`.