The correct answer is: Standard BOD is measured at 20°C – 5 days.
BOD stands for Biochemical Oxygen Demand. It is a measure of the amount of oxygen that is used by microorganisms to break down organic matter in water. The higher the BOD, the more organic matter is present in the water and the more polluted it is.
Standard BOD is measured at 20°C for 5 days. This is because 20°C is the temperature at which most microorganisms are most active and 5 days is the amount of time it takes for most microorganisms to break down organic matter.
BOD is an important measure of water quality because it can indicate the presence of pollution. High BOD levels can cause fish kills and other problems in aquatic ecosystems.