The correct answer is option (a) warm water holds less oxygen.
Thermal pollution refers to the increase in the temperature of water bodies like lakes, rives or oceans due to the discharge of heated liquid or hot air. This affects the aquatic organisms as they have a specific temperature requirement for their survival. This also affects the other parameters of the water body, of which, dissolved oxygen has a higher impact.
The warm temperature of the water body holds less dissolved oxygen than the water at the normal temperature. This gradually creates an anaerobic environment inside the water body killing fishes and other aquatic organisms.
Thus, thermal pollution kills fishes primarily because warm water holds less oxygen.
