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Water pollution, BOD and COD

55 questions on Water pollution, BOD and COD from the Environmental Chemistry chapter: 11 NEET level, 22 JEE Main, 22 JEE Advanced. Each one opens with its answer and solution.

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According to the standard NCERT treatment, the minimum dissolved oxygen needed for good growth of fish in a water body is about: NEET level
Biochemical oxygen demand (BOD) of a water sample is the: NEET level
Following the standard NCERT treatment, clean water has a BOD value: NEET level
Itai-itai disease, which causes severe bone and joint pain and kidney damage, is caused by contamination of water and food with: NEET level
Minamata disease results from poisoning by: NEET level
Eutrophication of a lake is mainly brought about by an excess of: NEET level
Prolonged use of drinking water having a fluoride concentration well above 2 ppm causes: NEET level
Methemoglobinemia (blue baby syndrome) in infants is caused by drinking water containing excess: NEET level
In the determination of chemical oxygen demand (COD), the organic matter of the sample is oxidised using: NEET level
The increase in the concentration of DDT in organisms at successively higher trophic levels of a food chain is called: NEET level
Detergents that produce a persistent foam in rivers and lakes are those having: NEET level
Following the standard NCERT treatment, a river sample is found to have a BOD of 25 ppm. It is best described as: JEE Main level
After a bloom of algae in a pond, the dissolved oxygen of the water falls sharply because: JEE Main level
The standard BOD test is carried out by incubating the sample for: JEE Main level
Glucose in a waste stream is oxidised completely: C6H12O6 + 6O2 -> 6CO2 + 6H2O. Taking C = 12, H = 1, O = 16, the mass of oxygen needed to oxidise 18.0 g of glu... JEE Main level
Discharge of hot water from a power plant into a river harms fish mainly because warm water: JEE Main level
Match the pollutant (Column I) with the effect (Column II). Column I: P = cadmium, Q = nitrate in drinking water, R = fluoride, S = methylmercury. Column II: 1 ... JEE Main level
Assertion (A): The COD of a sewage sample is generally greater than its BOD. Reason (R): Dichromate in acid oxidises organic matter that bacteria do not oxidise... JEE Main level
The persistence of DDT in the environment and its biomagnification are mainly due to the fact that DDT: JEE Main level
According to the international standards table used in the standard NCERT treatment, the permissible pH range of drinking water is: JEE Main level
Following the standard NCERT treatment, the maximum permitted concentration of lead in drinking water is: JEE Main level
Just downstream of the point where untreated sewage enters a river, the water shows: JEE Main level
In a COD determination, the excess dichromate that remains after oxidising the sample is determined by back titration with a standard solution of: JEE Main level
Phosphate-containing builders in detergents are objectionable mainly because they: JEE Main level
Assertion (A): Cold water usually contains more dissolved oxygen than warm water. Reason (R): The solubility of gases in water increases as the temperature rise... JEE Main level
Assertion (A): Soft (biodegradable) detergents are preferred to hard detergents. Reason (R): Soft detergents have unbranched hydrocarbon chains that bacteria ca... JEE Main level
Assertion (A): Chlorination of drinking water removes dissolved heavy metal ions such as Pb^2+. Reason (R): Chlorine kills pathogenic bacteria in water. JEE Main level
Match the standard value (Column I) with the quantity (Column II). Column I: P = BOD of clean water, Q = BOD of heavily polluted water, R = dissolved oxygen for... JEE Main level
Match the source of pollution (Column I) with its characteristic effect (Column II). Column I: P = phosphate in run-off, Q = oil spill, R = hot effluent from a ... JEE Main level
Which of the following water-borne diseases is correctly paired with its type of causative agent? JEE Main level
Drinking water is allowed a lead content of 50 ppb (that is, 50 mug per litre). The mass of lead in 2.0 L of water at exactly this limit is: JEE Main level
A water sample has an initial dissolved oxygen of 8.8 ppm, which falls to 4.9 ppm after incubation for 5 days at 20 degC (no dilution). Using the standard NCERT... JEE Main level
Inorganic mercury discharged into a bay is dangerous to people who eat fish from it mainly because anaerobic bacteria in the sediment: JEE Main level
Three water samples gave the following data (in ppm). Sample A: BOD 2, COD 5. Sample B: BOD 21, COD 34. Sample C: BOD 3, COD 120. Using the standard NCERT limit... JEE Advanced level
A stagnant lake has zero dissolved oxygen at the bottom, black mud, and a smell of rotten eggs. The gas responsible and its origin are: JEE Advanced level
A waste stream contains 45 mg L^-1 of glucose as its only organic matter. Take C = 12, H = 1, O = 16 and complete oxidation C6H12O6 + 6O2 -> 6CO2 + 6H2O. If bac... JEE Advanced level
Arrange the events of the eutrophication of a lake in the correct order: (i) fish die, (ii) fertiliser and detergent run-off adds nitrate and phosphate, (iii) d... JEE Advanced level
Groundwater of a village is analysed: pH 7.4, fluoride 4.2 ppm, nitrate 30 ppm, lead 20 ppb. Use these standard limits: pH 5.5 to 9.5, fluoride 1 ppm (above 2 p... JEE Advanced level
Industrial effluent was acidified and treated with H2S to give a yellow precipitate. The precipitate was insoluble in yellow ammonium sulfide, but dissolved in ... JEE Advanced level
A pollutant in drinking water from old pipes gives a yellow precipitate with potassium iodide, Pb^2+ + 2I^- -> PbI2, which dissolves in hot water and reappears ... JEE Advanced level
In a COD test, a sample consumes 1.20 mmol of K2Cr2O7 per litre. Take 1 mol of K2Cr2O7 as equivalent to 1.5 mol of O2 (O = 16). The COD of the sample is: JEE Advanced level
In a food chain the DDT concentrations (in ppm) are: water 0.00005, plankton 0.04, small fish 0.5, large fish 2.0, fish-eating bird 25. Which step has the large... JEE Advanced level
A 12.0 mL portion of waste water is made up to 300 mL with oxygen-saturated dilution water. The diluted mixture has dissolved oxygen of 8.7 mg L^-1 at the start... JEE Advanced level
In a COD determination, 25.0 mL of a sample is refluxed with 20.0 mL of 0.250 N K2Cr2O7 in acid. The unused dichromate requires 14.6 mL of 0.100 N ferrous ammon... JEE Advanced level
Select the correct statements about BOD and COD. JEE Advanced level
Select the correct statements about eutrophication. JEE Advanced level
Select the correctly matched pairs of pollutant and disease. JEE Advanced level
According to the standard values of the NCERT treatment, select the correct statements. JEE Advanced level
Select the correct statements about pesticides and detergents. JEE Advanced level
Select the correct statements about thermal pollution of a river by a power plant. JEE Advanced level
Sample P has BOD 3 ppm and dissolved oxygen 7.5 ppm. Sample Q has BOD 20 ppm and dissolved oxygen 2.5 ppm. Use these limits: clean water BOD below 5 ppm, pollut... JEE Advanced level
A waste water contains 90 mg L^-1 of glucose (C = 12, H = 1, O = 16), oxidised by C6H12O6 + 6O2 -> 6CO2 + 6H2O. Select the correct statements. JEE Advanced level
Select the correct statements about water treatment. JEE Advanced level
Select the correct statements about the dichromate reaction in COD determination, Cr2O7^2- + 14H+ + 6e^- -> 2Cr^3+ + 7H2O. JEE Advanced level
Select the correct statements about sewage and other sources of water pollution. JEE Advanced level