Paddle wheel aerator belongs to:

Correct option is B

Correct Answer: (b) Surface aerators
Explanation:
→ Paddle-wheel aerators operate at the water surface to agitate and entrain air, transferring oxygen into the pond — they are a common surface aerator type used in aquaculture.
→ They create large-scale circulation and increase dissolved oxygen effectively in shallow ponds.
Information Booster:
→ Selection depends on pond depth, area and power availability; paddle wheels are energy-efficient for many shrimp/fish farms.
Additional Information (Other Options):
(a) Gravity: passive designs; (c) turbine: different mechanism; (d) submersible: located below surface (different class).