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# Multiple choice question for engineering

## Set 1

1. _____ is the amount of oxygen required to oxidize only organic matter in sewage.
a) Turbidity
b) BOD
c) COD
d) DO

Answer: b [Reason:] BOD is the amount of oxygen required to oxidize only organic matter in sewage. It is always less than COD as COD oxidizes both organic and inorganic matter.

2. The full form of BOD is
a) Biodegradable oxygen demand
b) Biological oxygen demand
c) Biochemical oxygen demand
d) Bandwidth on demand

Answer: c [Reason:] The full form of BOD is biochemical oxygen demand. It is measured in ppm or mg/L.

3. The biochemical oxygen demand is computed by
a) Dissolved oxygen / Dilution factor
b) Dissolved oxygen + Dilution factor
c) Dissolved oxygen – Dilution factor
d) Dissolved oxygen * Dilution factor

Answer: d [Reason:] BOD = Dissolved oxygen * Dilution factor. Where, Dilution factor = Volume of diluted sewage sample / Volume of undiluted sewage sample.

4. State whether the following statement is true or false.
The value of deoxygenation constant is independent of the temperature.
a) True
b) False

Answer: b [Reason:] The value of deoxygenation constant is directly proportional to the temperature. It increases with increase in temperature. Figure 71.1: BOD vs time curve

Answer question 5 to 10 using the above figure.

5. Which of the following represents the first stage BOD?
a) ZR
b) RL
c) ZL
d) EP

Answer: c [Reason:] ZL represents the first stage BOD from the given figure. The first stage BOD is also called as the carbonaceous demand.

6. Which of the following represents the second stage BOD?
a) LP
b) RL
c) ZL
d) EP

Answer: a [Reason:] LP represents the second stage BOD from the given figure. The second stage BOD is also called as the nitrogenous demand.

7. The carbonaceous demand occurs due to oxidation of
a) Ammonia
b) Sulfur
c) Organic matter
d) Nitrogen

Answer: c [Reason:] The carbonaceous demand occurs due to oxidation of organic matter. The carbonaceous demand is also called as the initial demand.

8. The nitrogenous demand occurs due to oxidation of
a) Ammonia
b) Sulfur
c) Organic matter
d) Nitrogen

Answer: a [Reason:] The carbonaceous demand occurs due to oxidation of ammonia. The nitrogenous demand is also called as the final demand.

9. Which of the following is correctly matched?
a) ZR – Carbonaceous demand
b) RE – Nitrogenous demand
c) EP – Final demand
d) ZP – Combined demand

Answer: d [Reason:] ZP is correctly paired and it represents the combined demand, which includes both carbonaceous and nitrogenous demand.

10. The nitrogenous demand begins after how many days?
a) 1
b) 2
c) 3
d) 5

Answer: d [Reason:] As the growth rate of nitrifying bacteria is slow, the nitrogenous demand begins after 5 days.

## Set 2

Answer question 1-7 using the figure given below. Figure 75.1: Oxygen sag curve

1. The yellow curve represents
a) Deoxygenation curve
b) Reoxygenation curve
c) Oxygen sag curve
d) Equilibrium concentration of oxygen

Answer: a [Reason:] The yellow curve represents the deoxygenation curve, which depicts the depletion of dissolved oxygen in the absence of aeration.

2. Which of the following is represented by the green curve?
a) Deoxygenation curve
b) Reoxygenation curve
c) Oxygen sag curve
d) Equilibrium concentration of oxygen

Answer: b [Reason:] The green curve represents the reoxygenation curve, which depicts the supply of oxygen from the atmosphere to counterbalance the oxygen deficit.

3. The maximum deficiency of dissolved oxygen is represented by
a) Dotted blue line
b) Green curve
c) Yellow curve
d) Violet curve

Answer: a [Reason:] The maximum deficiency of dissolved oxygen is represented by the dotted blue line. It is finding with respect to the equilibrium concentration of oxygen.

4. Which of the following represents the oxygen sag curve?
a) Dotted blue line
b) Green curve
c) Yellow curve
d) Red curve

Answer: d [Reason:] The oxygen sag curve is represented by the red curve. It is also called as an oxygen deficit curve.

5. The oxygen deficit is maximum when
a) Rate of reaeration is 0
b) Rate of deoxygenation is 0
c) Rate of reaeration equals the rate of deoxygenation
d) Rate of reaeration > rate of deoxygenation

Answer: c [Reason:] The rate of oxygen deficit is the sum of the rate of reaeration and the rate of deoxygenation and it is maximum when the rate of reaeration equals the rate of deoxygenation.

6. When the BOD of wastewater increases, then
a) Rate of reaeration decreases
b) Rate of oxygen deficit increases
c) Rate of oxygen deficit decreases
d) Amount of oxygen in wastewater increases

Answer: b [Reason:] When the BOD of wastewater increases, the amount of dissolved oxygen decreases, so the rate of oxygen deficit increases.

7. State whether the following statement is true or false.
Rate of aeration is independent of the D.O content of wastewater.
a) True
b) False

Answer: b [Reason:] Rate of aeration = -(Rate of dissolved oxygen in water) which implies that the rate of aeration increases with increase in reduction of dissolved oxygen from wastewater.

8. The reoxygenation constant at temperature ‘T’ is expressed by
a) KRT = KR20 (1.016)T
b) KRT = KR20 (1.047) T-20
c) KRT = KR20 (1.016)T-20
d) KRT = KR20 (1.047)T

Answer: c [Reason:] The reoxygenation constant at temperature ‘T’, KRT = KR20 (1.016)T-20, where KR20 is the reoxygenation constant at 20oC.

## Set 3

1. The size of suspended solids lies in the range of ________
a) 10-3 – 10-6 mm
b) 103 – 106 mm
c) 10-1 – 10-3 mm
d) 101 – 103 mm

Answer: c [Reason:] Size of suspended solids – 10-1 – 10-3 mm, size of colloidal solids – 10-3 – 10-6 mm, size of dissolved solids – < 10-6 mm.

2. Suspended solids are measured by which of the following?
a) Turbidity rod
b) Gravimetric test
c) Chromatography
d) Jackson’s turbidity meter

Answer: b [Reason:] Turbidity rod and Jackson’s turbidity meter is used to find turbidity whereas chromatography is used to detect odour . Hence b is the correct answer.

3. The maximum permissible limit for suspended solids is ___
a) 10 mg/l
b) 20 mg/l
c) 30 mg/l
d) 40 mg/l

Answer: c [Reason:] The maximum permissible limit for suspended solids is 30mg/l for testing waste water which is set by the Environmental Protection Agency (EPA).

4. Identify the correct relation between the following?
a) Dissolved solid = Total solid + Suspended solid
b) Dissolved solid = Total solid – Suspended solid
c) Total solid = Dissolved solid / Suspended solid
d) Dissolved solid = Suspended solid – Total solid

Answer: b [Reason:] Dissolved solid is the difference between total solid and suspended solid. Suspended solid is non-filterable solid whereas dissolved solid is filterable solid.

5. Which method is used to measure the color of water?
a) Gravimetric analysis
b) Chromatography
c) Tintometer method
d) Hydrometer analysis

Answer: c [Reason:] The colors in water are measured by Tintometer method.It is measured on Burgess scale or cobalt scale by Nessler’s tube.

6. 1 TCU (True Color Unit) is equivalent to _____
a) The color produced by 1 g of platinum cobalt
b) The color produced by 1 mg of platinum cobalt
c) The color produced by 1 mg of platinum cobalt in 1L of distilled water
d) The color produced by 1 mg of platinum cobalt in 1mL of distilled water

Answer: c [Reason:] 1 TCU (True Color Unit) is equivalent to color produced by 1 mg of platinum cobalt in 1L of distilled water. The true color unit is also called as Hazen unit.

7. The range for threshold odour number is
a) 0-3
b) 1-5
c) 1-3
d) 0-5

Answer: c [Reason:] The maximum value of Threshold odour number is 3 and its range is 1-3. The threshold odour number is used to measure the intensity of taste and odour.

8. State whether the following statement is True or False.
Threshold odour number testing is preferred in hot water.
a) True
b) False

Answer: b [Reason:] TON testing is preferred in cold water as in hot water due to increase in temperature, taste and odour can change.

9. One JTU is equivalent to turbidity produced by
a) 1mg of fine silica dissolved in 1L of distilled water
b) 1g of fine silica dissolved in 1L of distilled water
c) 1g of fine silica dissolved in 1ml of distilled water
d) 1mg of fine silica dissolved in 1ml of distilled water

Answer: a [Reason:] 1 JTU is equivalent to turbidity produced by 1mg of fine silica dissolved in 1L of distilled water. It is called as Jackson’s turbidity unit and is based on absorption principle.

10. If the PO value is 6, what does it imply?
a) No perceptible odour
b) Very faint odour
c) Very distinct odour
d) Extremely strong odour

Answer: d [Reason:] The PO value indicates the odour intensity. 6 is the maximum PO value and it indicates extremely strong odour.

11. The range of temperature of water that is required to do the temperature test is__ 0C.
a) 10-25
b) 0-25
c) 10-30
d) 20-30

Answer: a [Reason:] To do the temperature test of water, its temperature should be between 100C and 250C and the temperature higher than 250C is considered objectionable.

12. Which of the following statement is wrong regarding turbidity?
a) It is an extent to which light is absorbed by particles in the water
b) It is expressed in ppm
c) It depends on the fineness of particle present in the water
d) Turbidity rod is a laboratory method to measure turbidity

Answer: d [Reason:] Turbidity rod is a field method not a laboratory method to measure turbidity.

13. The permissible limit of turbidity of domestic water is ____ ppm.
a) 5-10
b) 1-5
c) 10-50
d) 10-30

Answer: a [Reason:] According to WHO, the permissible limit for drinking water is 5NTU.

14. What is the full form of NTU in context with turbidity?
a) Number of transfer unit
b) Neurological turbidity unit
c) Nephelometric turbidity unit
d) Network terminal unit

Answer: c [Reason:] The value of turbidity measured by nephelometer is expressed in terms of NTU. Sometimes, it is referred as FTU or Formazin turbidity unit.

15. When depth of insertion of turbidity rod increases, the reading in the turbidity rod ___
a) Decreases
b) Increases
c) First decrease, then increase
d) Remains constant

Answer: a [Reason:] Turbidity rod is inserted inside the water and the reading at which needle becomes invisible gives the turbidity.

## Set 4

1. Which of the following represents the physical characteristics of water?
a) Chloride content
b) BOD
c) Turbidity
d) COD

Answer: c [Reason:] Turbidity represents the physical characteristic of water, whereas BOD, COD and chloride content represents the chemical characteristic of water.

2. Which of the following is measured in mg/L?
a) Unit weight
b) Coefficient of cohesion
c) Discharge
d) Turbidity

Answer: d [Reason:] The turbidity of waste water is measured in mg/L. The other units of turbidity are ppm, NTU and JTU.

3. Which of the following instrument is used to measure turbidity?
a) Olfactometer
b) Turbidity meter
c) Colorimeter
d) Spectrophotometer

Answer: b [Reason:] Turbidity can be measured by Jackson’s turbidity meter, Baylis turbidity meter, turbidity rod and Nephelometer.

4. When the sewage becomes stronger, the turbidity of wastewater
a) Increases
b) Decreases
c) Becomes constant
d) Slightly decrease

Answer: a [Reason:] When the sewage becomes stronger, the milkiness in water increases and thus, the turbidity increases.

5. Which color indicates the fresh sewage?
a) Pink
b) Red
c) Black
d) Grey

Answer: d [Reason:] If the color of sewage is grey, yellow and light brown, then it means that the sewage is fresh.

6. The color of the septic sewage is
a) Pink
b) Red
c) Black
d) Grey

Answer: c [Reason:] The color of septic sewage is black or dark brown. It contains either little or no oxygen.

7. The odor in wastewater is measured by
a) Osmoscope
b) Chromatography
c) Olfactometer
d) Turbidity meter

Answer: a [Reason:] The odor in waste water is measured by Osmoscope which consist of two 10mm diameter glass tubes which is 300mm long and 8mm wide.

8. In India, the average temperature of sewage is
a) 10oC
b) 20oC
c) 40oC
d) 80oC

Answer: b [Reason:] The average temperature of sewage is 20oC. The temperature of sewage is higher than that of the water supply.

9. Identify the incorrect statement from the following?
a) High odor intensity indicates odorless water
b) Fresh sewage is odorless
c) Turbidity can be measured by turbidity rod
d) NTU is a unit of turbidity

Answer: a [Reason:] If the odor intensity of water is 6, it indicates extremely strong odor and when it is 0, it indicates the odorless water.

10. _______ indicates the freshness of sewage.
a) Turbidity
b) Color
c) Temperature
d) COD

Answer: b [Reason:] The color indicates the freshness of sewage. It can be detected easily by the naked eye.

11. ______ represents the number of dilutions required to reduce odor.
a) Dispersion
b) Threshold odor number
c) BOD
d) COD

Answer: b [Reason:] The threshold odor number is equal to the volume of samples of water required to add to 100 units of odorless fresh water at which the mixture gives the first detectable odor.

12. The odor quality of Amines is
a) Rotten egg
b) Fishy
c) Fecal matter
d) Decayed cabbage

Answer: b [Reason:] The odor quality of Amines is fishy and its chemical formula is CH3NH2.

13. The odor quality of compound is ammoniacal. Identify the type of compound from the following options.
a) Acetic acid
b) Benzene
c) Ammonia
d) Methane

Answer: c [Reason:] Ammonia has an ammoniacal type of odor quality and its chemical formula is NH3.

14. The wastewater from the kitchen is an example of
a) Black water
b) Yellow water
c) Green water
d) Grey water

Answer: d [Reason:] The wastewater from the kitchen is an example of grey water. It also includes water from the bathroom without urine and feces.

15. The type of wastewater from the flushing operation of toilet is
a) Green water
b) Red water
c) Black water
d) Brown water

Answer: c [Reason:] The type of wastewater from the flushing operation of toilet is black in color and if it does not include urine, then it is brown in color.

## Set 5

1. The pollution zones in the river are divided into how many types?
a) 3
b) 4
c) 6
d) 8

Answer: b [Reason:] There are 4 types of pollution zones in the river, namely zone of degradation, zone of active decomposition, zone of recovery and zone of clear water.

2. In which pollution zone of river, growth of algae reappear?
a) Zone of degradation
b) Zone of recovery
c) Zone of active decomposition
d) Zone of clean water

Answer: b [Reason:] The growth of algae reappear in the zone of recovery.The growth of fungi decreases.

3. In which pollution zone of the river, the dissolved oxygen reduced to 0?
a) Zone of degradation
b) Zone of recovery
c) Zone of clean water
d) Zone of active decomposition

Answer: d [Reason:] The dissolved oxygen, reduced to 0 in the zone of active decomposition. The water is highly polluted in this zone.

4. Which is the third zone of pollution in the river?
a) Zone of recovery
b) Zone of degradation
c) Zone of clean water
d) Zone of active decomposition

Answer: a [Reason:] The zone of recovery is the third zone of pollution in the river where river tries to recover the polluted water through the self purification process.

5. In which pollution zone of the river, water retains its original dissolved oxygen concentration?
a) Zone of degradation
b) Zone of recovery
c) Zone of active decomposition
d) Zone of clean water

Answer: d [Reason:] The water retains its original dissolved oxygen concentration in the zone of clean water. It has a clear appearance.

6. The fishes were present in the river, but algaes were not able to survive. What is the zone of pollution of the river?
a) Zone of recovery
b) Zone of degradation
c) Zone of clean water
d) Zone of active decomposition

Answer: b [Reason:] It is the zone of degradation as dissolved oxygen has reduced to its 40%. The fishes will die when dissolved oxygen is less than 4ppm.

7. In which pollution zone of the river, the concentration of D.O reduced to 40%?
a) Zone of degradation
b) Zone of recovery
c) Zone of active decomposition
d) Zone of clean water