Tag: water pollution

Questions Related to water pollution

Which of the following is/are correct statement(s) regarding increasing population as a reason for water scarcity?

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  1. Increasing population creates demand for construction of houses, shops, offices, roads and pavements.

  2. This decreases the open areas like parks, and playgrounds.

  3. This in turn decreases the seepage of rainwater into ground.

  4. A pukka floor does not allow water to seep in easily, while in a grass lawn water seeps through in no time.

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Correct Option: A,B,C,D
Explanation:

All of the following are correct statements regarding increasing population as a reason for water scarcity.
Increasing population creates demand for construction of houses, shops, offices, roads and pavements.
This decreases the open areas like parks, and playgrounds.
This in turn decreases the seepage of rainwater into ground.
A pukka floor does not allow water to seep in easily, while in a grass lawn water seeps through in no time.

Which of the following is a measurement of water pollution ?

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  1. PSC

  2. PCB

  3. BOD

  4. COD

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Correct Option: C
Explanation:

  1. Polar stratospheric clouds (PSCs) are the medium on which reservoir chlorine compounds are converted into ozone-destroying chlorine radicals, they are essentially two types of  PSC known as type 1 and type 2.
  2. Polychlorinated biphenyl (PCBs) is a group of organic compounds used in the manufacture of plastics, as lubricants, in transformers, adhesives and so forth. They are highly toxic to aquatic life and persist in the environment for long periods of time. They can accumulate in food chains and may produce harmful side-effects at high concentrations.
  3. 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.
  4. Chemical oxygen demand (COD) is defined as a  measure of the oxygen equivalent of the organic matter content of a sample that is susceptible to oxidation by a strong chemical oxidant. Therefore, BOD is a measurement of water pollution.

Option (C) is correct.

Which of the following statement is false?

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  1. Lower the concentration of D.O., the more polluted is the water sample

  2. The tolerable limit of lead in drinking water is $50\ ppm$

  3. Water is considered pure if it has BOD less than $5\ ppm$

  4. In COD determination, the pollutants resistant to microbial oxidation are not oxidized by an oxidizing agent like $K _{2}Cr _{2}O _{7}$

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Correct Option: D
Explanation:

In COD, the degradation is affected by an oxidizing agent, $K _2 Cr _2 O _7.$ COD  is a measure of amount of oxygen , required to degrade or breakdown the organic matter. 

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:

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  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:

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  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?

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  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.