Question

Which of the following is determined by the oxidation of acidified potassium dichromate?
A. DO
B. BOD
C. COD
D. TLV

Answer 1

Hint: Chemical measures of water quality include dissolved oxygen (DO), chemical oxygen demand (COD), biochemical oxygen demand (BOD), total dissolved solids (TDS), pH, nutrients (nitrates and phosphorus), heavy metals, soil chemicals (including copper, zinc, cadmium, lead and mercury) and pesticides.

Complete answer:
The minimum level of toxic pollutants present in the atmosphere which affects a person adversely when he is exposed to 7 to 8 hours in a day is called TLV.
Biochemical oxygen demand (BOD) is the amount of dissolved oxygen needed (i.e. demanded) by aerobic biological organisms to break down organic material present in a given water sample at a certain temperature over a specific time period.
BOD = Number of mg of oxygen molecules​ required / number of litres of water sample.
BOD = Parts of oxygen / million parts of water sample.
Chemical oxygen demand (COD) test is commonly used to indirectly measure the amount of organic compounds in water. In environmental chemistry, the chemical oxygen demand (COD) is an indicative measure of the amount of oxygen that can be consumed by reactions in a measured solution. It is commonly expressed in mass of oxygen consumed over volume of solution which in SI units is milligrams per litre (\[mg/L\] ).
In COD, most commonly, a \[0.25N\] solution of potassium dichromate is used for COD determination, although for samples with COD below \[50\;mg/L\] , a lower concentration of potassium dichromate is preferred. The chemical oxygen demand of a sample is determined by the oxidation process of the potassium dichromate.

Thus, the correct option is C.

Note:
The most common application of COD is in quantifying the amount of oxidizable pollutants found in surface water (e.g. lakes and rivers) or wastewater. COD is useful in terms of water quality by providing a metric to determine the effect an effluent will have on the receiving body, much like biochemical oxygen demand (BOD).