Chemical Oxygen Demand (COD) is a measure of
All organic matters in water
Chemical Oxygen Demand (COD) is an important water quality parameter used to assess the level of pollution in a water body.
COD measures the total amount of oxygen required to chemically oxidize ALL the organic matter present in a water sample - this includes both biodegradable organic matter (which microorganisms can break down) as well as non-biodegradable or refractory organic matter (which cannot be easily broken down biologically, such as certain industrial pollutants).
This is different from Biochemical Oxygen Demand (BOD), which only measures the oxygen consumed by microorganisms while decomposing biodegradable organic matter - BOD does not account for non-biodegradable organic compounds.
Because COD uses a strong chemical oxidizing agent (such as potassium dichromate) to oxidize organic matter, it captures a more complete picture of total organic pollution, covering both biodegradable and non-biodegradable fractions.
Therefore, "inorganic matters in water" is wrong since COD targets organic, not inorganic, matter; "all chemicals present in water" is too broad and incorrect; and "only some specific organic matters" is incomplete since COD covers ALL organic matter, not just specific ones.
The correct answer is that COD measures all organic matters in water.
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