Match the following Group IGroup 2P. Thickening of sludge1.

Match the following

Group I	Group 2
P. Thickening of sludge	1. Decrease in volume of sludge by chemical oxidation
Q. Stabilization of sludge	2. Separation of water by heat or chemical treatment
R. Conditioning of sludge	3. Digestion of sludge
S. Reduction of sludge	4. Separation of water by flotation or gravity

1. P- 4, Q-3, R-1, S-2
2. P- 3, Q-2, R-4, S-1
3. P- 4, Q-3, R-2, S-1
4. P- 2, Q-1, R-3, S-4