Explanation:

Correct Option: (b) Explanation:  Option (b) is correct Supplementary Notes Thermal pollution  Thermal pollution is the rise or fall in the temperature of a natural aquatic environment caused by human in fl uence.  Thermal pollution is caused by either dumping hot water from factories and power plants or removing trees and vegetation that shade streams, permitting sunlight to raise the temperature of these waters, release of cold water which lowers the temperature.  The change in temperature impacts organisms by decreasing oxygen supply. Warm water contains less oxygen. Elevated temperature typically decreases the level of dissolved oxygen (DO) in water.  So there is decrease in rate of decomposition of organic matter. Green algae are replaced by less desirable blue green algae.  It also increases the metabolic rate of aquatic animals, results in consumption of more food in a shorter time than if their environment were not changed.  An increased metabolic rate may result in food source shortages, causing a sharp decrease in a population.  Primary producers are affected by warm water because higher water temperature increases plant growth rates, resulting in a shorter life span and species overpopulation.  This can cause an algae bloom which reduces the oxygen levels in the water. The higher plant density results in reduced light intensity, decreases photosynthesis and leads to an increased plant respiration rate. This is similar to the eutrophication.  It also effects ecosystem composition as changes in the environment may also result in a migration of organisms to another more suitable environment which leads to competition for fewer resources thereby compromising food chains of the old and new environments.