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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3ev155

Select the correct statements about BOD and COD.

AA high BOD means a high amount of dissolved oxygen is available to fish
BIn the COD method the excess dichromate is titrated against a standard oxidising agent
CBOD is determined from the oxygen consumed by microorganisms in a sample incubated for 5 days at 20 $^{\circ}$ C
DCOD is expressed as mg of oxygen per litre equivalent to the dichromate consumed

Answer: C, D

BOD

_{5}

uses 5 days at 20

^{\circ}

C, and COD is reported as mg

O X_{2}

per litre equivalent to dichromate used. The excess dichromate is back titrated with a reducing agent,

Fe X^{2 +}

, not an oxidising agent. A high BOD means much oxidisable matter that will consume oxygen, so it is bad for fish.

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