Concept:A water pollutant is any substance that causes harmful changes in water quality, but oxygen gas is essential for aquatic life.
Explanation:Oxygen gas dissolves in water as
O2 and is required by fish and other aquatic organisms for respiration.
It is not a water pollutant because it supports life rather than contaminating the water.
Inorganic fertilizers pollute water by introducing excess nutrients such as nitrates and phosphates.
These nutrients can cause eutrophication, which harms aquatic ecosystems.
Warm water affluent raises the temperature of water bodies and reduces the amount of dissolved oxygen available.
Biodegradable waste is a pollutant because its decomposition by microorganisms increases the biological oxygen demand and lowers oxygen levels.
Among the given options, oxygen gas is the only substance that is not considered a water pollutant.
Answer:C. Oxygen gas