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Multiple choice question for engineering

Set 1

1. When turbidity in water increases, the efficiency of chlorine
a) Decreases
b) Increases
c) Slightly increases
d) Remains constant

View Answer

Answer: a [Reason:] The presence of turbidity in water makes it difficult to obtain free residual chlorine. So, it is preferred to apply chlorine after filtration when water is free from turbidity.

2. The presence of metallic compounds in water _______ the efficiency of chlorine.
a) Decreases
b) Increases
c) Slightly decreases
d) Remains constant

View Answer

Answer: a [Reason:] The presence of metallic compounds like iron and manganese utilized large amount of chlorine and decrease the efficiency of chlorine for disinfection.

3. The amount of hypochlorous acid formed when pH of water is 8 is
a) 95% of total free chlorine
b) 80% of total free chlorine
c) 30% of total free chlorine
d) 5% of total free chlorine

View Answer

Answer: c [Reason:] When chlorine is added to water, the amount of hypocholorous acid decreases as pH of water increases. It is 95% of total free chlorine when pH < 6.7 and 30% of total free chlorine when pH of water is 8.

Question 4 and 5 are based on the following diagram given below.
environmental-engineering-assessment-questions-answers-q4
Figure: Kill rates of E-coli

4. Which type of chlorine is represented by the green line as shown in figure?
a) Free residual chlorine
b) Ammonia chlorine
c) Combined residual chlorine
d) Residual chloramine

View Answer

Answer: a [Reason:] Free residual chlorine composed of dissolved hypochlorite ions, hypochlorous acid and chlorine gas present in water. It is represented by the green line in the above figure.

5. Which type of chlorine is represented by the red line as shown in figure?
a) Free residual chlorine
b) Ammonia chlorine
c) Combined residual chlorine
d) Residual chloramine

View Answer

Answer: b [Reason:] Ammonia chlorine is represented by the red line in the figure which results in speedy disinfection, it contains ammonia and chlorine in the ratio of 1:1 in the following figure.

6. The efficiency of chlorine increase by
a) Presence of metallic compounds
b) When the pH of the water increases
c) When the pH of the water decreases
d) Turbid water

View Answer

Answer: c [Reason:] The efficiency of chlorine is inversely proportional to the pH of water. When the pH of the water containing chlorine decreases, the efficiency of chlorine increases.

7. The contact time for disinfection by free chlorine is
a) 20 minutes
b) 30 minutes
c) 40 minutes
d) 60minutes

View Answer

Answer: a [Reason:] The contact time for disinfection by free chlorine is 20 minutes and it depends on pH, temperature, type and concentration of microorganism.

8. The contact time for disinfection by combined chlorine is
a) 20 minutes
b) 30 minutes
c) 40 minutes
d) 60minutes

View Answer

Answer: d [Reason:] The contact time for disinfection by combined chlorine is 60 minutes. The % kill of bacteria depends upon the time of contact between chlorine and microorganism.

Set 2

1. Chlorides are estimated by titration with a standard silver nitrate solution by using _______as indicator.
a) Potassium manganate
b) Potassium chloride
c) Potassium chromate
d) Potassium dichromate

View Answer

Answer: c [Reason:] 2-3 drops of potassium chromate are added to appropriate amount of water sample and then it is titrated with a standard solution of silver nitrate.

2. State whether the following statement is True or False.
Carbonate hardness can be removed by adding lime to water.
a) True
b) False

View Answer

Answer: a [Reason:] Carbonate hardness is due to the presence of carbonates and bicarbonates of calcium and magnesium in water and can be removed by boiling or by adding lime to it.

3. Which of the following statement is wrong regarding permanent hardness?
a) It is also called carbonate hardness
b) It is due to the presence of sulfates, chlorides and nitrates of calcium and magnesium
c) It cannot be removed by boiling
d) It requires special methods of water softening to get removed

View Answer

Answer: a [Reason:] Permanent hardness is called non-carbonate hardness whereas temporary hardness is called carbonate hardness.

4. One degree of hardness is equivalent to ___ ppm
a) 2
b) 1
c) 10
d) 100

View Answer

Answer: b [Reason:] Water is said to have one degree of hardness when its soap destroying power is equivalent to the effect of 14.25mg of calcium carbonate in one litre of water.

5.

Degree of hardnessNature of water
1Extremely soft water
2Very soft water
3Soft water
9?

What can be filled in place of the question mark in the above table?
a) Excessive hard water
b) Reasonably soft water
c) Very hard water
d) Hard water

View Answer

Answer: d [Reason:] When the degree of hardness is 9, then it indicates the hard water. For excessive hard water, it is 15 and for very hard water, it is 11.

6. In which method of determining total hardness of water is based on the premise that hardness producing substance react with soap and form insoluble compounds before lather is produced?
a) Clark’s method
b) Hehner’s method
c) Versenate method
d) EDTA method

View Answer

Answer: a [Reason:] In Clark’s method, total hardness is found by determining the standard soap solution required to obtain permanent lather with the water sample of known volume.

7. What is the indicator used in EDTA method?
a) Potassium chromate
b) Potassium dichromate
c) Potassium chloride
d) Erio chrome, black T

View Answer

Answer: d [Reason:] Hardness is determined by using Ethylene diamine tetra-acetic acid using Erio chrome, black T as indicator at a pH between 8.5 and 11.

8. The permissible limit of pH preferred for potable water is ___ppm.
a) 6.5-9
b) 7-8.5
c) 10-14
d) 0-7

View Answer

Answer: a [Reason:] The permissible limit of pH for potable water should not exceed 9 and should not be less than 6.5 and the preferred limit is 7-8.5.

9. Given list 1 and list 2, find which of the following pair is correctly matched?

List 1 (Chemical substance)List 2 (Permissible limit in ppm)
A. Lead1. 0.05
B. Phenol2. 0.001
C. Zinc3. 0.01
D. Chromium4. 5
5. 0.2

a) A-5
b) B-3
c) C-4
d) D-2

View Answer

Answer: c [Reason:] Lead has a permissible limit of 0.05ppm, phenol has 0.001ppm, zinc has 5ppm and chromium has a permissible limit of 0.05ppm in water.

10. What is the concentration of H+ ions in moles/L in water if the pOH value is 6?
a) 10-6
b) 10-7
c) 10-8
d) 10-9

View Answer

Answer: c [Reason:] pH + pOH = 14 pOH = 6, so pH = 14-6= 8 H+ = 10-pH = 10-8moles/L.

Set 3

1. In which of the following filters, the rate of filtration is highest?
a) Slow sand filter
b) Rapid sand filter
c) Pressure filter
d) Roughing filter

View Answer

Answer: c [Reason:] The rate of filtration is highest in pressure filter and its filtration rate lies between 6000 to 15000 litres per hour per m2 of filter area while in rapid sand and roughing filter, it is between 6000 to 8000 litres per hour per m2 of filter area.

2. The final loss of head in slow sand filter is ______ than rapid sand filter.
a) Higher
b) Lower
c) Slightly Lower
d) Equivalent

View Answer

Answer: b [Reason:] The loss of head in slow sand filter lies between 15-100cm and of rapid sand filter lies between 30-300cm.The final loss of head in slow sand filter is 100cm while in rapid sand filter is 300cm.

3. The turbidity of water applied to rapid sand filter is less than _______
a) 35-40ppm
b) 10-20ppm
c) 30-40ppm
d) 10-15ppm

View Answer

Answer: a [Reason:] As before filtration, sedimentation and coagulation process is done, so the turbidity of water should be less than 35-40ppm.

4. The period of cleaning of a slow sand filter is ______ than rapid sand filter.
a) Smaller
b) Larger
c) Slightly smaller
d) Slightly larger

View Answer

Answer: b [Reason:] The period of cleaning of a slow sand filter is 1-2 months and that of the rapid sand filter is 2-3 days.

5. The bacterial removal efficiency of the rapid sand filter is ______ in comparison to slow sand filter.
a) More
b) Less
c) Equal
d) Better

View Answer

Answer: b [Reason:] The bacterial removal efficiency of the rapid sand filter is90-99%, whereas of a slow sand filter is 98-99%.

6. How is the grain size distribution of sand in rapid sand filter?
a) Stratified
b) Unlayered
c) Layered with heaviest grains at the top
d) Layered with lightest grains at the top

View Answer

Answer: d [Reason:] The grain size distribution of sand in rapid sand filter is stratified with lightest grains at the top and heaviest grains at the bottom.

7. Consider the following statement
1. The penetration of suspended matter is deep in the slow sand filter
2. The penetration of suspended matter is superficial in the rapid sand filter
3. Coagulation is not required in the slow sand filter
Which of the above statement is/are correct?
a) Only 3
b) 1, 2
c) 1, 2, 3
d) 2, 3

View Answer

Answer: a [Reason:] The penetration of suspended matter is deep in rapid sand filter, whereas the penetration of suspended matter is superficial in slow sand filter.

8. Consider the following statement
1. The slow sand filter is not efficient in removing turbidity
2. The slow sand filter has a high initial cost
3. Skilled supervision is required in slow sand filter
Which of the above statement is/are correct?
a) Only 3
b) 1, 2
c) 1, 2, 3
d) 2, 3

View Answer

Answer: b [Reason:] Skilled supervision is not required in slow sand filter but it is essential in the case of the rapid sand filter.

9. The filter run in rapid sand filter should not be less than _____ hours.
a) 1
b) 6
c) 12
d) 24

View Answer

Answer: d [Reason:] The filter run in rapid sand filter should not be less than 24 hours and its head loss should not exceed 2m.

10. Consider the following statement
1. Slow sand filter is not flexible in variation in demand
2. The rapid sand filter is flexible in fluctuations in demand
3. The method of cleaning of a slow sand filter involves agitation and back-washing
Which of the above statement is/are correct?
a) 1, 2
b) 1, 2, 3
c) 2, 3
d) Only 3

View Answer

Answer: a [Reason:] The method of cleaning of a slow sand filter involves scrapping of top layer to 15 to 25mm whereas in rapid sand filter involves agitation and back-washing.

11. State whether the following statement is true or false.
Rapid sand filters are very efficient in removal of color.
a) True
b) False

View Answer

Answer: a [Reason:] Rapid sand filters are very efficient in removal of color and the intensity of color can be brought down below 3 on cobalt scale.

Set 4

1. Iron and Manganese are generally present in water supplies as
a) Suspension
b) Solution
c) Colloidal particles
d) Either suspension or solution

View Answer

Answer: d [Reason:] Iron and Manganese are generally present in water supplies in the form of hydrated oxide as suspension and bicarbonates as a solution.

2. What concentration of iron and manganese will cause unpleasant taste and odor of water?
a) 1ppm
b) 2ppm
c) 3ppm
d) >3ppm

View Answer

Answer: d [Reason:] When the concentration of iron and manganese is greater than 3, it will result in unpleasant taste and odor, unwanted precipitation and difficulties in manufacturing processes.

3. The presence of Sulfate iron in the water results in
a) Odorless water
b) Acidity in water
c) Colorless water
d) Growth of crenothrix in water mains

View Answer

Answer: b [Reason:] The presence of Sulfate iron in the water results in acidity in water and corrosiveness on iron and brass.

4. The reddish tinge in the water is due to the presence
a) Zinc
b) Copper
c) Iron
d) Manganese

View Answer

Answer: c [Reason:] The reddish tinge in the water is due to the presence of iron. Water contains iron by the reaction of CO2 in contact with iron ore forming soluble ferrous bicarbonate.

5. The brown tinge in the water is due to the presence
a) Zinc
b) Copper
c) Iron
d) Manganese

View Answer

Answer: d [Reason:] The brown tinge in the water is due to the presence of manganese, which occurs when it is present in an amount greater than 0.3ppm.

6. By aeration process, dissolved iron is oxidized into
a) Ferrous oxide
b) Ferric oxide
c) Ferrous hydroxide
d) Ferric hydroxide

View Answer

Answer: b [Reason:] By aeration process, dissolved iron is oxidized into ferric oxide, which is insoluble in water.

7. By which process dissolved manganese compounds can be converted into insoluble manganese compounds?
a) Aeration
b) Coagulation
c) Sedimentation
d) Flocculation

View Answer

Answer: a [Reason:] The dissolved manganese compounds can be converted into insoluble manganese compounds by aeration The precipitated floc can be settled down in settling tanks.

8. For removal of iron from water, ________ mg of oxygen is required.
a) 0.14
b) 0.50
c) 1
d) 1.5

View Answer

Answer: a [Reason:] The reaction for removal of iron from water is – 4Fe + O2 + 10H2O = 4Fe (OH)3 +8H 1mg of Fe requires 0.14 mg of O2.

9. For removal of manganese from water, ________ mg of oxygen is required.
a) 0.14
b) 0.50
c) 0.29
d) 0.90

View Answer

Answer: c [Reason:] The reaction for removal of manganese from water is – 4Mn + 3O2 + 6H2O = 6MnO2 +12H 1mg of Mn requires 0.29 mg of O2.

10. Removal of manganese from water takes place at a pH of ______
a) 1.5
b) 3
c) 6
d) 9.4

View Answer

Answer: d [Reason:] Removal of manganese from water takes place at a pH between 9.4 to 9.6. Pre- chlorination up to 0.7 to 1 mg/l affect the oxidation and precipitation of manganese.

11. When small amounts of iron and manganese are present in water, they are removed by
a) Aeration
b) Coagulation
c) Manganese zeolite
d) Filtration

View Answer

Answer: c [Reason:] When small amounts of iron and manganese are present in water, they are removed by manganese zeolite where iron and manganese are oxidized to insoluble hydrated oxides which are removed by filtration action of zeolite bed.

12. Removal of iron from water takes place at a pH of ______
a) 1.5
b) 3
c) 8.2
d) 9.4

View Answer

Answer: d [Reason:] Removal of iron from water takes place at a pH of 8.2. It can be removed in an oxidized condition by softening water by the excess lime process.

13. The taste produced by microorganism, can be controlled by
a) Potassium per-manganate
b) Potassium dichromate
c) Sodium chloride
d) Iodine

View Answer

Answer: a [Reason:] The taste produced by microorganism, can be controlled by potassium per-manganate. It can be controlled alone or in combination with chlorine.

14. Which of the following regarding ozonation is incorrect?
a) Improves the appearance of water
b) Removes traces of color
c) Remove odor
d) Remove phenolic and algae taste

View Answer

Answer: d [Reason:] Ozonation improves the appearance of water, removes traces of color, remove odor and is also effective against earthy and moldy tastes and odor.

Set 5

1. Which of the following is used for the control of taste and odor in water?
a) Sedimentation
b) Coagulation
c) Filtration
d) Activated carbon

View Answer

Answer: d [Reason:] Activated carbon is used for the control of taste and odor, which has resulted from the presence of dissolved gases.

2. Granular activated carbon has a surface area of
a) 100-200m2/g
b) 500-1400m2/g
c) 400-600m2/g
d) 500-900m2/g

View Answer

Answer: b [Reason:] Granular activated carbon has a surface area of 500-1400m2/g. Higher surface area is the prime consideration in adsorption.

3. _______ is produced by passing a carbonaceous material through a heating mechanism at high temperature.
a) Potassium per-manganate
b) Potassium dichromate
c) Activated carbon
d) Iodine

View Answer

Answer: c [Reason:] Activated carbon is produced by passing a carbonaceous material through the heating mechanism at high temperature against air, steam, chlorine and flue gases.

4. Which of the following is a carbonaceous material?
a) Charcoal
b) Petroleum
c) Hydrogen sulfide
d) Sodium chloride

View Answer

Answer: a [Reason:] Charcoal is a carbonaceous material. Various other carbonaceous materials are coke, paper, char and sawdust.

5. Which of the following is not a property of activated carbon?
a) It is impermeable
b) It has many carbon atoms with free valencies
c) It is available in granular as well as powder form
d) It has a prolonged suspension

View Answer

Answer: a [Reason:] Activated carbon is very porous. It should have prolonged suspension, easily wettable and effective odor absorption capacity.

6. The thickness of the activated carbon filter bed is
a) 10-20cm
b) 30-80cm
c) 75-100cm
d) 40-50cm

View Answer

Answer: c [Reason:] The thickness of the activated carbon filter bed is between 75 to 100 cm which is supported on 35-50 cm thick graded gravel bed.

7. When activated carbon is applied at more than one point, then it is called ________
a) Dual treatment
b) Split treatment
c) Sludge treatment
d) Carbonaceous treatment

View Answer

Answer: b [Reason:] The activated carbon in powder form can be applied to the water before, during or after coagulation at more than one point, which is called as split treatment.

8. State whether the following statement is true or false.
Activated carbon in powder form is applied in the mixing basin.
a) True
b) False

View Answer

Answer: a [Reason:] Activated carbon in powder form can be applied in the mixing basin either alone or fixed with other chemicals like alum by means of a dry chemical feed machine.

9. Activated carbon can be applied to raw water ______ treatment process.
a) During
b) Ahead of
c) Before
d) After

View Answer

Answer: b [Reason:] Activated carbon can be applied in various ways like ahead of the treatment process, in the mixing basin or after filtration. Its rate of application is high when the filter is washed.

10. The dose of activated carbon in powdered form is controlled by
a) Chromatography
b) Distillation
c) Threshold odor test
d) MPN test

View Answer

Answer: c [Reason:] The dose of activated carbon in powdered form is controlled by threshold odor test. For effective use, the dose must be adequate, thoroughly mixed and time of contact should be long.

11. What is the dose of copper sulfate required for the treatment of water?
a) 0.3-0.6ppm
b) 2-6ppm
c) 4-8ppm
d) 10-20ppm

View Answer

Answer: a [Reason:] Copper sulfate is used for the removal of odor, taste and color from water and the dose required varies from 0.3 to 0.6ppm.

12. There are protozoa present in the water. Its name is Dinobryen. What is the dose of copper sulfate required to kill it?
a) 0.02ppm
b) 0.3ppm
c) 0.5ppm
d) 0.8ppm

View Answer

Answer: b [Reason:] Dinobryen produces an aromatic, violet and fishy odor and the dose of copper sulfate required to kill it is 0.3ppm.