250+ TOP MCQs on Types of Settling and Answers

Environmental Engineering Multiple Choice Questions on “Types of Settling”.

1. How many types of settling are there in the sedimentation tank?
a) 3
b) 4
c) 5
d) 6
Answer: b
Clarification: There are 4 types of settling in the sedimentation tank, namely Flocculent, Discrete, Compression and Hindered settling.

2. In which type of settling, sedimentation of discrete particles takes place?
a) Zone settling
b) Compression settling
c) Hindered settling
d) Discrete settling
Answer: d
Clarification: In Discrete settling, sedimentation of discrete particles takes place where the particles have little tendency to flocculate.

3. The settling velocity of spherical particle is given by ____________
a) Darcy Weisbach equation
b) Hazen and William equation
c) Stokes equation
d) Bernoulli’s equation
Answer: c
Clarification: The settling velocity of spherical particle is given by stokes equation where vS = (g/18) * (G-1) d2 /v when diameter d is less than 0.1mm.

4. In the expression vS = 1.8 (g*d (G-1))1/2, the diameter of spherical particle is ____________
a) 0.1mm
b) < 0.1mm
c) 1mm
d) >1mm
Answer: d
Clarification: The settling velocity of spherical particle is given by stokes law and when the diameter d of spherical particle is > 1mm, settling velocity is given by vS = 1.8 (g*d (G-1))1/2 where G is the specific gravity of the particle.

5. In which type of settling, settling of particles takes place by the contact of impurities with each other present in wastewater?
a) Flocculent settling
b) Hindered settling
c) Compression settling
d) Discrete settling
Answer: c
Clarification: When large amounts of impurities are present in water, they contact each other in the compression zone and compression settling takes place.

6. _______ is formed when alum is added to sewage.
a) Acid
b) Floc
c) Salt
d) Base
Answer: b
Clarification: When a coagulant is added to sewage, then a gelatinous precipitate called floc is formed and flocculent settling takes place.

7. In which settling type, dilute suspension of particles takes place?
a) Zone settling
b) Compression settling
c) Hindered settling
d) Discrete settling
Answer: c
Clarification: In this type of settling, particle mass increases and it settles down due to flocculation.

250+ TOP MCQs on Air Pollutants and Answers

Environmental Engineering Multiple Choice Questions on “Air Pollutants”.

1. Which gas is mainly produced due to incomplete burning of wood?
a) CO
b) SO2
c) NO2
d) NO3
Answer: a
Clarification: CO is the colorless, odorless, toxic gas produced due to incomplete burning of wood.

2. Which of the following is involved in production of carboxy haemoglobin?
a) CO
b) SO2
c) NO2
d) NO3
Answer: a
Clarification: CO + Blood ——> Carboxy haemoglobin (Pink color).

3. Which of the following is a liquid form of aerosol?
a) Fume
b) Dust
c) Mist
d) Smoke
Answer: c
Clarification: Mist is a liquid form of aerosol whereas, Fume, Dust and Smoke are a solid form of aerosol.

4. X ray films are a source of which of the following gas?
a) SO2
b) CO2
c) NO2
d) SO3
Answer: c
Clarification: NO2 is produced from X ray film. It causes irritation to eyes and cause respiratory disease.

5. The maximum size of fly ash is ___________
a) 1μm
b) 100μm
c) 1000μm
d) 10μm
Answer: c
Clarification: Fly ash is a finely divided particle produced from the combustion of coal. Its maximum size is 1000μm.

6. Which of the following leads to a disease called broncho spasm?
a) SO2
b) SO3
c) SO4
d) CO2
Answer: b
Clarification: SO3 reacts with body fluids forming H2SO4 leading to Broncho spasm.

7. The minimum size of the smoke particle is ___________
a) 0.2μm
b) 1μm
c) 0.8μm
d) 0.5μm
Answer: d
Clarification: Smoke is produced due to incomplete combustion of coal. Its size lies between 0.5μm to 1μm.

8. Which of the following is a secondary air pollutant?
a) SPM
b) PAN
c) SO2
d) NO2
Answer: b
Clarification: Peroxy Acetyl Nitrate is a secondary air pollutant whereas, Suspended Particulate Matter, SO2 and NO2 are primary air pollutants.

9. The permissible concentration of PM 10 in the air is ___________
a) 60μg/m3
b) 40μg/m3
c) 50μg/m3
d) 20μg/m3
Answer: a
Clarification: The permissible concentration of PM 10 in air is 60μg/m3 whereas of PM 2.5 is 40μg/m3.

250+ TOP MCQs on Ozone Depletion and Answers

Environmental Science Multiple Choice Questions on “Ozone Depletion”.

1. What is the average concentration of ozone in the ozone layer of the atmosphere?
a) Nearly 100%
b) Greater than 90%
c) Between 10-50%
d) Less than 10ppm

Answer: d
Clarification: The concentration of ozone is about 10 ppm in the ozone layer and only 0.3 ppm in the entire atmosphere.

2. Who discovered the ozone layer?
a) Henri Buisson & Charles Fabry
b) Carl Sagan & Charles Fabry
c) G.M.B Dobson
d) Carl Sagan &G.M.B Dobson

Answer: a
Clarification: In 1913, Henri Buisson and Charles Fabry discovered the ozone layer and later its properties were studied by G.M.B. Dobson.

3. Which of the following devices can be used to measure ozone in the stratosphere from the ground?
a) Spectrometer
b) Photometer
c) Spectrophotometer
d) Spectro-ozonometer

Answer: c
Clarification: The spectrophotometer developed by Dobson can be used to measure ozone in the stratosphere from the ground. The amount of ozone is measured in terms of – Dobson unit.

4. The ozone layer absorbs what range of wavelengths of the sun’s radiation?
a) 0.80 nm – 1.50 nm
b) 200 nm – 315 nm
c) 450 nm – 570 nm
d) 600 nm – 750 nm

Answer: b
Clarification: The ozone layer absorbs the medium frequency UV radiations from the sun and hence protects the life forms at the surface from harm.

5. Who discovered the formation of ozone from photochemical reactions?
a) G.M.B Dobson
b) Sydney Chapman
c) Carl Sagan
d) Henri Buisson

Answer: a
Clarification: Sydney Chapman was the physicist who discovered that stratospheric ozone if formed when the UV rays from the sun splits oxygen molecules, and the nascent oxygen combines with existing molecules to form ozone.

6. Between what altitudes, is the ozone layer found in highest concentrations?
a) 10-20km
b) 20-40km
c) 40-55km
d) 55-70km

Answer: b
Clarification: The ozone layer is found in high concentrations of 2-8ppm at an altitude of 20-40km.

7. Nitrogen also helps in preventing UV rays from reaching the Earth.
a) True
b) False

Answer: a
Clarification: Nitrogen prevents extremely short wavelengths or vacuum UV radiations (10-100nm) from reaching the surface.

8. Which of the following UV radiations is responsible for causing sun burns and skin cancer?
a) UV-A
b) UV-B
c) UV-C
d) All of the mentioned

Answer: b
Clarification: UV-B radiations of 315-280nm is responsible for causing sunburns, genetic damage as well as skin cancer.

9. The long UV-B radiations are important for vitamin D production of the skin.
a) True
b) False

Answer: a
Clarification: The longest of the UV-B radiations reach the surface of the earth is small fractions and aids in vitamin D production of the skin.

10. In which season is the ozone found at its maximum level in the northern hemisphere?
a) Winter
b) Summer
c) Spring
d) Autumn

Answer: c
Clarification: The ozone levels in the northern hemisphere are at maximum during the spring season.

11. When was the ozone hole discovered?
a) 1974
b) 1964
c) 1994
d) 1984

Answer: d
Clarification: The ozone hole was discovered in the year 1984 by Jonathan Franklin, Joseph Farman and Brian Gardiner.

12. The ozone hole is a phenomenon that has occurred in:
a) Arctic region
b) Northern temperate region
c) Southern temperate region
d) None of the mentioned

Answer: d
Clarification: The phenomenon of the ozone hole occurred in the Antarctic region primarily due to catalytic breakdown of ozone molecules by halogenated compounds.

13. Which of the following chemicals are responsible for the depletion of the stratospheric ozone layer?
a) Refrigerants
b) Propellants
c) Foam-blowing agents
d) All of the mentioned

Answer: d
Clarification: Refrigerants containing halocarbons, foam-blowing agents such as HFCs, halons, CFCs and freons as well as propellants containing halogenated compounds are responsible for depleting the ozone layer.

14. What does EESC stand for in context of ozone depleting compounds?
a) Equivalent Effective Stratospheric Chlorine
b) Equivalent Effective Stratospheric Chlorofluorocarbons
c) Equivalent Energy Saving Compounds
d) Energy Effective Stratospheric Compounds

Answer: a
Clarification: EESC stands for equivalent effective stratospheric chlorine is used to measure the chlorine equivalent of halogens that can deplete the ozone layer.

15. The Montreal Protocol bans the production of which of the following chemical substances?
a) Chlorine, bromine, CFCs, freons
b) Carbon tetrachloride, halons, trichloroethane, CFCs
c) CFCs, bromine, halons, freons
d) CFCs, halons, freons

Answer: b
Clarification: The Montreal protocol bans the production of halons, trichloroethane, CFCs and carbon tetrachloride.