Biochemical oxygen demand (BOD) of a water body is used as an indicator of:
Correct: B
BOD is defined as the amount of dissolved oxygen required by aerobic biological organisms to break down organic material present in a given water sample at a certain temperature over a specific time period (usually 5 days at 20°C). A high BOD indicates that a large amount of organic matter is present in the water, which is decomposed by aerobic bacteria that consume dissolved oxygen, leading to oxygen depletion and potentially causing fish kills. BOD is a key parameter in assessing water pollution and eutrophication.