In what process and under what environmental conditions would a mesophyll cell of a flowering plant give out oxygen ?

It will be Mesophyll because

Explanation:

The primary and the absolute most important role of the mesophyll is its role in photosynthesis. Photosynthesis, as you may know, is the process by which a plant takes carbon dioxide, water, and sunlight and creates sugars, which result in the plant having energy.

it's diluted or concentrated

in a diluted solution, you can add a lot more solute but in concentrated only a little more can be added