Choose the correct option bod stands for

BOD • It stands for Biochemical Oxygen Demand. • “The amount of oxygen required by bacteria to break down the organic matter present in a certain volume of a sample of water is called Biochemical Oxygen Demand” BOD value of water • A BOD number of less than 5 ppm indicates that the water is clean. • A BOD value of 17 ppm or above indicates that the water is extremely polluted. Hence BOD stands for Biochemical Oxygen Demand.

The correct options are A B O D will be more for that sample in which a higher amount of organic waste is present C A sample with lower B O D is more suitable for aquatic life D B O D will be higher for that sample of water which has more number of microorganisms present in the sample • Biochemical oxygen demand increases as the organic waste increases, which is consumed by microorganisms. • If BOD is higher it means that the dissolved oxygen is less for aquatic life.

Explanation: Bio-chemical oxygen demand: (i) Biochemical oxygen demand is used as a measure of the quantity of oxygen required for oxidation of biodegradable organic matter present in water sample by aerobic biological action. BOD at any time is given by, BOD t= L o(1 - 10 -K dt)---(i) Where, L o= Ultimate BOD For BOD 5, t = 5 days Assume K d= 0.1 day -1(Generally taken) Then from (i), BOD 5= L o(1 - 10 -5 × 0.1) = 0.68× L o BOD 5/L o= 0.68 ≈ 2/3 • Hence the BOD of water during 5 days at 20°C is generally taken as the standard and is about 68% of the total demand i.e. ultimate BOD. 10 Days BOD ia about 10% of the total.