when does the paramecium pump out more water, when there is a high salt concentration or when there is a low salt concentration surrounding the paramecium?

The correct answer is - when there is a low salt concentration

Explanation:

Water moves through osmosis which means water moves from an area having low solute concentration to an area having high solute concentration through a semipermeable membrane.

So in a hypotonic solution, the concentration of solute in the environment surrounding the paramecium will be low than in paramecium which allows water to move inside paramecium.

The more the water moves in the paramecium the more water will be pumped by the contractile vacuole present in the paramecium. Therefore the correct answer is - when there is a low salt concentration.