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Biochemical Oxygen Demand (BOD) is a measure of organic material present in water. BOD value less than 5 ppm indicates a water to be ________.

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  1. rich in dissolved oxygen

  2. poor in dissolved oxygen

  3. highly polluted

  4. not suitable for aquatic life

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Correct Option: A
Explanation:

Clean water has BOD which is less than 5 ppm. If it is equal to or more than 12 ppm, then the water is considered as polluted. So this indicates water be rich in dissolved oxygen, that helps the microorganisms to oxidize inorganic and organic materials. 

Pollution of lakes and rivers affects aquatic life. Fish cannot live in water that has oxygen less than $4$ milligrams per liter. Other freshwater aquatic life (including anaerobic bacteria) also cannot survive without adequate oxygen. 'BOD' stands for:

chemistry water too little to waste pollution of water water pollution planet earth

  1. Biological oxygen demand

  2. Bacterial oxygen deficit

  3. Basic oxygen demand

  4. Building oxygen deposits

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Correct Option: A
Explanation:
BOD stands for Biological Oxygen Demand is the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material present in a given water sample at a certain temperature over a specific time period.

Clean water would have Biochemical oxygen demand (BOD) value of less than:

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  1. 17 ppm

  2. 5 ppm

  3. 200,000 ppm

  4. 10 ppm

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Correct Option: B
Explanation:
A water supply with a BOD level of 3-5 ppm is considered moderately clean. In water with a BOD level of 6-9 ppm, the water is considered somewhat polluted because there is usually organic matter present and bacteria are decomposing this waste.
Hence, clean water would have a BOD value of less than 5.

Hence, the correct option is $\text{B}$

Biological Oxygen Demand (BOD) can be defined as:

chemistry water too little to waste pollution of water water pollution planet earth

  1. the amount of oxygen required by bacteria to break down the organic matter of a sample of water

  2. the amount of chemicals required to break down the organic matter of a sample of water

  3. the amount of phosphate required to oxidise the organic matter of a sample of water

  4. the amount of organic matter present in the given sample of water

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Correct Option: A
Explanation:

BOD refers to the dissolved oxygen that the microorganisms like bacteria need to oxidize, means to break down inorganic and organic matter in water. It is a measure of water quality. 

What does $BO{D} _{5}$ represent?

chemistry water too little to waste pollution of water water pollution planet earth

  1. Biological oxygen demand in five days

  2. Dissolved oxygem left after five days

  3. Dissolved oxygen consumed in five days

  4. Microorganisms killed by ozone in sewage treatment plants in five hours

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Correct Option: A
Explanation:

$BO{ D } _{ 5 }$ stands for 5-day Biochemical Oxygen Demand. The BOD test measures, oxygen is used as microbes breathe as they eat the contaminants  in wastewater.

10 mL of water required 1.47 mg of $K _{2}Cr _{2}O _{7}$ (M. wt. = 294) for oxidation of dissolved organic matter in presence of acid. Then the C.O.D of water sample is:

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  1. 2.44 ppm

  2. 24 ppm

  3. 32 ppm

  4. 1.6 ppm

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Correct Option: B
Explanation:

$ Number \  of   \ milliequivalent $ = $\dfrac{weight \ in \ mg}{Equivalent\  weight}$


= $\dfrac{1.47}{294/6}$ = $0.03meq$

$\therefore$COD of sample is:

$\dfrac{0.03}{10}\times 1000$ =  $3meq/L$

In terms of Oxygen COD is :

$3 meq/L \times  (8 mg O _2/meq)$ = $24 mg/L= 24ppm$

Option B is correct.