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CPCB Scientist B practice questions

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Question 1Air Quality Management

Under the National Ambient Air Quality Standards (NAAQS) notified by CPCB, what is the 24-hour average standard for PM2.5 in residential, rural and other areas?

  1. 40 µg/m³
  2. 100 µg/m³
  3. 30 µg/m³
  4. 60 µg/m³ Correct answer.

Explanation

The notified NAAQS set the PM2.5 24-hour limit at 60 µg/m³ for residential, rural and other areas, with an annual limit of 40 µg/m³. The higher 24-hour value reflects short-term episodic peaks rather than chronic exposure. Values such as 40 µg/m³ apply to the annual averaging period.

Question 2Air Quality Management

Which pollutant in the NAAQS is expressed as an 8-hour average and is also a precursor for tropospheric ozone formation?

  1. Nitrogen dioxide Correct answer.
  2. Lead
  3. Sulphur dioxide
  4. Carbon monoxide

Explanation

Nitrogen dioxide has both annual and 24-hour standards, and photolysis of NO2 is the key step that generates ozone in the troposphere. It is therefore both a regulated pollutant and an ozone precursor. Sulphur dioxide and lead are not the primary ozone precursors in this scheme.

Question 3Air Quality Management

In the Air Quality Index used by CPCB, a sub-index value of 350 for a pollutant places the overall AQI category in which band?

  1. Very Poor Correct answer.
  2. Poor
  3. Moderate
  4. Severe

Explanation

The CPCB AQI bands are 0–50 Good, 51–100 Satisfactory, 101–200 Moderate, 201–300 Poor, 301–400 Very Poor and 401–500 Severe. A sub-index of 350 falls in the 301–400 range, so the category is Very Poor. The overall AQI is the maximum of the pollutant sub-indices.

Question 4Air Quality Management

Which reference method is conventionally used for measuring ambient sulphur dioxide in Indian monitoring networks?

  1. High volume sampling with gravimetry
  2. Beta attenuation
  3. Chemiluminescence
  4. Improved West and Gaeke method Correct answer.

Explanation

Sulphur dioxide is conventionally monitored by the improved West and Gaeke colorimetric method, in which SO2 is absorbed in a solution and estimated spectrophotometrically. Gravimetric high volume sampling and beta attenuation are used for particulate matter. Chemiluminescence is used for oxides of nitrogen.

Question 5Air Quality Management

Which atmospheric stability condition most favours the trapping of pollutants near the ground?

  1. Temperature inversion Correct answer.
  2. Superadiabatic lapse rate
  3. Strong mechanical turbulence
  4. Neutral lapse rate

Explanation

A temperature inversion places warmer air above cooler surface air, suppressing vertical mixing so that emissions accumulate in a shallow layer. Superadiabatic and neutral conditions promote dispersion rather than trapping. Strong mechanical turbulence also enhances dilution.

Question 6Air Quality Management

Which gas is the principal precursor that reacts with nitrogen oxides under sunlight to produce tropospheric ozone?

  1. Volatile organic compounds Correct answer.
  2. Nitrous oxide
  3. Carbon dioxide
  4. Methane only

Explanation

Tropospheric ozone is produced in photochemical smog when volatile organic compounds are oxidised in the presence of NOx and sunlight. Methane is a VOC but is not the principal precursor category referred to in regulatory photochemical modelling. Carbon dioxide and nitrous oxide are not ozone precursors in this cycle.

Question 7Air Quality Management

Which of the following is a primary air pollutant?

  1. Peroxyacetyl nitrate
  2. Nitric acid
  3. Ozone
  4. Sulphur dioxide Correct answer.

Explanation

Primary pollutants are emitted directly from a source, and sulphur dioxide is emitted directly by combustion of sulphur-bearing fuels. Ozone, peroxyacetyl nitrate and nitric acid are formed in the atmosphere by chemical reactions and are secondary pollutants.

Question 8Air Quality Management

Which size fraction is sampled by a PM10 inlet at ambient conditions?

  1. Total suspended particulate matter
  2. All particles smaller than 2.5 µm
  3. Particles larger than 10 µm only
  4. Particles with aerodynamic diameter of 10 µm or less at 50 percent cut efficiency Correct answer.

Explanation

A PM10 inlet is designed so that 50 percent of particles of 10 µm aerodynamic diameter pass to the filter, giving a cut-point convention rather than a sharp cutoff. It is not restricted to the fine fraction. Total suspended particulate matter uses a different inlet.

Question 9Air Quality Management

A stack emitting at 30 m height has a plume rise of 45 m. Using the effective stack height, what is the effective release height used in the Gaussian dispersion equation?

  1. 15 m
  2. 30 m
  3. 45 m
  4. 75 m Correct answer.

Explanation

Effective stack height is the sum of physical stack height and plume rise, giving 30 + 45 = 75 m. This effective height is used as the release elevation in Gaussian plume models. Subtracting the values or using either alone misrepresents the buoyant release.

Question 10Air Quality Management

In the Gaussian plume model, doubling the horizontal dispersion coefficient σy while keeping all else constant has what effect on the centreline ground-level concentration?

  1. It leaves the concentration unchanged
  2. It halves the concentration Correct answer.
  3. It quadruples the concentration
  4. It doubles the concentration

Explanation

The centreline concentration is inversely proportional to the product σy·σz, so doubling σy alone halves the concentration. Greater horizontal spread dilutes the same mass flux over a wider cross-section. The relationship is reciprocal, not proportional.

Question 11Air Quality Management

Which condition corresponds to the Pasquill stability class F?

  1. Strong daytime insolation with moderate wind
  2. Clear night with light wind Correct answer.
  3. Clear day with strong wind
  4. Overcast day with strong wind

Explanation

Pasquill class F denotes very stable conditions, which occur on clear nights with light winds when radiative cooling produces a strong inversion. Strong daytime insolation produces unstable classes such as A or B. Overcast or windy conditions tend toward neutral classes.

Question 12Air Quality Management

In an urban airshed, the ozone concentration peaks in the afternoon while NOx peaks during the morning traffic period. Which explanation best accounts for this?

  1. NOx is destroyed by sunlight before ozone forms
  2. Ozone is emitted directly by vehicles in the afternoon
  3. Photochemical production requires sunlight and builds up as the day progresses Correct answer.
  4. Ozone is removed by deposition only at night

Explanation

Ozone is a secondary pollutant whose production depends on photolysis, so concentrations build through the day and peak after several hours of sunlight. Morning NOx emissions provide the precursor reservoir that fuels this afternoon production. The lag reflects photochemistry rather than direct emission.

Question 13Air Quality Management

Which approach is used to apportion measured ambient PM2.5 to sources using chemical composition data and source profiles?

  1. Gaussian plume modelling
  2. Air quality index computation
  3. Emission inventory interpolation
  4. Receptor modelling with chemical mass balance Correct answer.

Explanation

Chemical mass balance is a receptor model that uses measured chemical species concentrations and source profiles to estimate source contributions. It works backward from ambient measurements rather than forward from emissions. Gaussian plume modelling and inventories are source-oriented approaches.

Question 14Air Quality Management

A monitoring station records PM2.5 of 120 µg/m³ over 24 hours. Using the CPCB 24-hour standard of 60 µg/m³, what is the exceedance factor?

  1. 6.0
  2. 1.2
  3. 0.5
  4. 2.0 Correct answer.

Explanation

The exceedance factor is the measured concentration divided by the standard, giving 120/60 = 2.0. This ratio expresses how many times the standard is exceeded. It is a simple ratio, not a percentage or difference.

Question 15Air Quality Management

Which process is the dominant removal pathway for gaseous pollutants such as sulphur dioxide and nitrogen dioxide from the troposphere?

  1. Photodissociation into inert gases
  2. Radioactive decay
  3. Wet and dry deposition after oxidation to acids Correct answer.
  4. Sedimentation under gravity

Explanation

SO2 and NO2 are oxidised to sulphuric and nitric acid and then removed by wet deposition in rain or dry deposition to surfaces. Sedimentation is significant only for particles, not gases. These gases do not decay radioactively or photolyse into inert products.

Question 16Air Quality Management

Which statement correctly distinguishes the National Air Quality Monitoring Programme objectives from the AQI reporting function?

  1. NAMP applies only to industrial stacks and not ambient air
  2. NAMP generates monitoring data while the AQI converts sub-indices into a public communication index Correct answer.
  3. The AQI generates monitoring data while NAMP communicates health risk
  4. Both perform identical functions with different names

Explanation

NAMP is the ambient monitoring network that produces concentration data across stations. The AQI is a derived reporting tool that converts pollutant sub-indices into a single easily understood category for public communication. The two serve distinct but linked functions.

Question 17Air Quality Management

Which factor most strongly increases ground-level concentrations from a given elevated point source?

  1. Increased atmospheric turbulence
  2. Increased mixing height
  3. Increased wind speed
  4. Reduced plume buoyancy with stable conditions Correct answer.

Explanation

Stable conditions suppress vertical mixing and reduce plume rise, so the plume stays close to the ground and concentrations rise. Higher wind speed and mixing height dilute pollutants. Increased turbulence also enhances dispersion and lowers concentrations.

Question 18Air Quality Management

Which measurement principle underlies the beta attenuation monitor used for continuous PM monitoring?

  1. Light scattering by individual particles
  2. Absorption of infrared radiation by gases
  3. Attenuation of beta radiation by deposited particulate mass on a filter tape Correct answer.
  4. Electrochemical oxidation of gases at an electrode

Explanation

A beta attenuation monitor measures the reduction in beta particle transmission through a filter as particulate mass collects on it, giving a mass-based estimate. Light scattering is a different optical technique. Infrared absorption and electrochemical cells target gases rather than particulate mass.

Question 19Air Quality Management

A city wants to assess whether a new bypass road improved air quality near a residential area. Which design gives the strongest causal evidence?

  1. Relying on modelled emissions alone
  2. Comparing the residential site with an industrial site
  3. A single post-project measurement campaign
  4. A before-after comparison with a parallel control site unaffected by the road Correct answer.

Explanation

A before-after comparison with a control site accounts for seasonal and background changes that would otherwise confound the effect of the road. A single campaign or a comparison with an unrelated site cannot separate the intervention effect. Emissions modelling alone does not verify measured air quality.

Question 20Air Quality Management

Under the CPCB AQI scheme, which pollutant sub-index is not included because it lacks a defined averaging standard in the index?

  1. PM10
  2. Ozone
  3. Carbon monoxide
  4. Ammonia Correct answer.

Explanation

The CPCB AQI is computed from eight pollutants: PM10, PM2.5, NO2, SO2, CO, O3, NH3 and Pb. Ammonia is included in the index with defined breakpoints, so the premise of exclusion is the trap; among the options, the index does include NH3 and the others. Care must be taken because the question tests knowledge of the index composition.

Question 21Air Quality Management

In a Gaussian plume model, the ground-level centreline concentration at downwind distance x is proportional to which combination?

  1. Q/(u σy σz) Correct answer.
  2. u/(Q σy σz)
  3. Q u σy σz
  4. Q σy σz/u

Explanation

The centreline ground-level concentration scales as Q divided by the product of wind speed and the two dispersion coefficients. Emission rate increases concentration while wind speed and dispersion dilute it. Inverting any of these terms reverses the physical dependence.

Question 22Air Quality Management

An airshed shows high NOx and low VOC concentrations, and ozone formation is found to decrease when NOx is reduced. This behaviour is characteristic of which regime?

  1. NOx-limited regime Correct answer.
  2. VOC-limited regime
  3. NOx-saturated regime
  4. Background ozone regime

Explanation

When ozone production falls as NOx is reduced, the chemistry is NOx-limited and NOx control is effective. In a NOx-saturated or VOC-limited regime, reducing NOx can initially increase ozone. The observed response therefore identifies the NOx-limited case.

Question 23Air Quality Management

Which statement correctly describes the relationship between the 24-hour and annual NAAQS for PM10 in India?

  1. The annual standard is higher than the 24-hour standard
  2. The 24-hour standard is 100 µg/m³ and the annual standard is 60 µg/m³ Correct answer.
  3. Only an annual standard exists for PM10
  4. Both standards are 60 µg/m³

Explanation

The notified PM10 standards are 100 µg/m³ for 24 hours and 60 µg/m³ annually in residential, rural and other areas. The 24-hour value is set higher to accommodate short-term peaks while the annual value controls chronic exposure. The annual limit cannot exceed the short-term limit in this framework.

Question 24Air Quality Management

A stack plume is released into a neutral boundary layer with strong winds. Which outcome is expected for maximum ground-level concentration compared with a calm stable night?

  1. Lower concentration because strong winds and neutral stability enhance dispersion Correct answer.
  2. Higher concentration because wind carries pollutants down
  3. Higher concentration because neutral air traps pollutants
  4. Equal concentration because emission rate is unchanged

Explanation

Strong winds increase the dilution term and neutral stability allows continued vertical mixing, both lowering ground-level concentration. Stable calm nights restrict mixing and produce higher concentrations. Emission rate alone does not determine concentration without accounting for dispersion.

Question 25Air Quality Management

Which combination of measurements is required to compute a chemical mass balance source apportionment for PM2.5?

  1. Emission inventory totals alone
  2. Ambient species concentrations and source chemical profiles Correct answer.
  3. Wind speed and stack height only
  4. AQI category and population density

Explanation

Chemical mass balance requires measured ambient concentrations of marker species and representative chemical profiles for each candidate source. It then solves for the contribution of each source profile. Meteorological or inventory data alone cannot apportion measured mass.

Question 26Air Quality Management

Under the CPCB National Ambient Air Quality Standards (2009), which averaging period applies to the lead (Pb) standard for ambient air?

  1. Only 1 hour
  2. 1 hour and 8 hours
  3. 24 hours and annual Correct answer.
  4. Only annual

Explanation

The 2009 NAAQS list lead with both a 24-hour limit of 1.0 µg/m³ and an annual limit of 0.5 µg/m³, measured as Pb in ambient air. Unlike several gaseous pollutants that carry 1-hour or 8-hour sub-indices, lead is regulated on these two averaging periods. This pair of values is what an ambient Pb monitoring programme is assessed against.

Question 27Air Quality Management

A CAAQMS reports an 8-hour average of 100 µg/m³ for PM2.5 and 100 µg/m³ for PM10. Using the CPCB AQI breakpoint tables, which statement about the two sub-indices is correct?

  1. The PM2.5 sub-index is higher because PM2.5 has lower breakpoint concentrations. Correct answer.
  2. Neither pollutant is assigned a sub-index because only 24-hour averages are used.
  3. Both sub-indices fall in the same AQI category and are numerically identical.
  4. The PM10 sub-index is higher because PM10 mass includes the PM2.5 fraction.

Explanation

The AQI sub-index is obtained by linear interpolation of the measured concentration within the CPCB breakpoint table for that pollutant and averaging time. Because PM2.5 breakpoints are set at much lower concentrations than PM10 breakpoints, equal mass concentrations do not give equal sub-indices. At 100 µg/m³ the PM2.5 sub-index is therefore markedly higher than the PM10 sub-index.

Question 28Air Quality Management

A tall stack releases a buoyant plume into a well-mixed convective daytime boundary layer. Compared with a stable night-time case for the same stack and wind speed, what is expected for the maximum ground-level concentration?

  1. It will be unchanged, since maximum concentration depends only on emission rate and wind speed.
  2. It will be higher and occur farther downwind because of reduced plume rise.
  3. It will be lower and occur farther downwind because of greater plume dispersion. Correct answer.
  4. It will be higher and occur closer to the stack because of enhanced vertical mixing.

Explanation

Strong daytime convection produces large dispersion coefficients and a deep mixing layer, so the plume is diluted over a greater volume. The maximum ground-level concentration is therefore reduced and is reached at a larger downwind distance. Stable night-time conditions confine the plume and typically give higher peak ground-level values nearer the source.

Question 29Air Quality Management

A regulator wants to reduce peak 1-hour NO2 concentrations near a busy intersection. Which control measure most directly targets the dominant near-road formation pathway for NO2?

  1. Reducing primary NO emissions from the vehicle fleet Correct answer.
  2. Limiting volatile organic compound emissions from solvents
  3. Scrubbing sulphur dioxide from nearby industrial stacks
  4. Controlling secondary particulate nitrate formation

Explanation

Near busy roads, NO2 arises largely from primary NO emitted in exhaust and its rapid oxidation by ambient ozone, so cutting fleet NO emissions lowers both terms at once. Controls on SO2, secondary nitrate or solvent VOCs act on other pollutants or slower pathways. They do not address the fresh vehicular NO-to-NO2 conversion that drives the near-road 1-hour peak.

Question 30Water Quality Management

Under the Water (Prevention and Control of Pollution) Act, 1974, which body is constituted at the State level to exercise the powers and perform the functions assigned to it under the Act?

  1. Central Ground Water Board
  2. State Water Resources Agency
  3. State Pollution Control Board Correct answer.
  4. District Environment Committee

Explanation

The 1974 Act provides for a Central Pollution Control Board at the national level and a State Pollution Control Board in each State, the latter being the body that consents, monitors and enforces for water pollution within the State. Other bodies may deal with water resources or groundwater but do not hold statutory consent powers under this Act.

Question 31Water Quality Management

The 'consent to establish' issued by a State Pollution Control Board under the Water Act is granted primarily to ensure that:

  1. The land use is converted to industrial use
  2. Pollution control measures are designed into the plant before construction begins Correct answer.
  3. The industry pays its water tariff before construction
  4. The industry registers its trade mark with the State

Explanation

Consent to establish is a pre-construction clearance intended to verify that effluent treatment and disposal arrangements are built into the project design. Consent to operate follows later and confirms that the installed facilities actually perform as required.

Question 32Water Quality Management

Biochemical oxygen demand measured over five days at 20 degrees Celsius (BOD5) primarily represents:

  1. The oxygen consumed by microorganisms oxidising biodegradable organic matter Correct answer.
  2. The total organic and inorganic carbon present in the sample
  3. The oxygen deficit caused by ammonia oxidation alone
  4. The dissolved oxygen remaining after chemical oxidation

Explanation

BOD5 measures the dissolved oxygen consumed by microorganisms while decomposing biodegradable organic matter under standard incubation conditions. It is a bioassay of oxygen demand, not a measure of total carbon or residual oxygen.

Question 33Water Quality Management

Which indicator organism group is conventionally used to detect recent faecal contamination of drinking water sources?

  1. Thermotolerant (faecal) coliforms such as E. coli Correct answer.
  2. Sulphate-reducing bacteria
  3. Total coliforms including soil organisms
  4. Iron-precipitating bacteria

Explanation

Thermotolerant coliforms, with E. coli as the key indicator, grow at elevated temperature and are largely of faecal origin, so their presence signals recent faecal contamination. Total coliforms include environmental species and are therefore less specific.

Question 34Water Quality Management

A sample has a 5-day BOD of 200 mg/L and a k (base e) of 0.23 per day at 20 degrees Celsius. Using first-order kinetics, the ultimate BOD is closest to:

  1. 290 mg/L Correct answer.
  2. 355 mg/L
  3. 320 mg/L
  4. 245 mg/L

Explanation

Ultimate BOD equals BOD5 divided by (1 minus e raised to minus k times 5). With k of 0.23, e raised to minus 1.15 is about 0.3166, so the denominator is about 0.6834 and the ultimate BOD is roughly 200 divided by 0.6834, close to 290 mg/L.

Question 35Water Quality Management

In a river, a wastewater outfall with high BOD typically produces which downstream dissolved oxygen profile?

  1. A sag reaching a minimum followed by gradual recovery Correct answer.
  2. No change because oxygen is conserved
  3. A monotonic decrease with no recovery zone
  4. An immediate rise followed by a fall

Explanation

Downstream of the outfall, oxygen demand from biodegradation exceeds reaeration, so dissolved oxygen falls to a critical minimum, after which reaeration and reduced demand allow recovery. This is the classical oxygen sag curve described by the Streeter-Phelps model.

Question 36Water Quality Management

A wastewater discharge of 0.5 cubic metres per second at BOD 300 mg/L mixes with a river flow of 9.5 cubic metres per second at BOD 2 mg/L. Assuming complete mixing, the downstream BOD is closest to:

  1. 14.9 mg/L Correct answer.
  2. 20.9 mg/L
  3. 18.9 mg/L
  4. 16.9 mg/L

Explanation

Mass balance gives the mixed concentration as the flow-weighted mean: (0.5 times 300 plus 9.5 times 2) divided by 10, which is (150 plus 19) divided by 10, or 16.9 mg/L. The value of 14.9 mg/L arises if the river background is wrongly ignored.

Question 37Water Quality Management

The term 'assimilative capacity' of a water body refers to:

  1. The total dissolved solids tolerated by irrigation
  2. The ability to receive pollutants without exceeding designated use criteria Correct answer.
  3. The volume of water stored behind a dam
  4. The maximum flow that a channel can carry

Explanation

Assimilative capacity is the pollutant load a water body can absorb while still meeting its designated best use and water quality standards. It underpins total maximum daily load and load-based consent allocations.

Question 38Water Quality Management

Under the CPCB designated best use classification, Class A water is designated for:

  1. Propagation of wildlife and fisheries
  2. Irrigation and industrial cooling
  3. Organised outdoor bathing Correct answer.
  4. Controlled waste disposal

Explanation

The designated best use scheme ranks uses by stringency, with Class A reserved for organised outdoor bathing and requiring the most stringent faecal coliform and dissolved oxygen criteria. Lower classes permit progressively less sensitive uses.

Question 39Water Quality Management

A stream is classified as Class C (drinking water source with conventional treatment). Which parameter set most directly governs whether the classification is met?

  1. Dissolved oxygen, faecal coliform and pH Correct answer.
  2. Sodium adsorption ratio and boron
  3. Chloride and sulphate only
  4. Colour and turbidity only

Explanation

For drinking water source classes, the decisive criteria are dissolved oxygen, faecal coliform density and pH, together with the conventional treatment assumption. Irrigation-specific indices such as sodium adsorption ratio are not part of that classification.

Question 40Water Quality Management

In the context of wastewater treatment, the term 'secondary treatment' conventionally refers to:

  1. Screening and grit removal
  2. Sludge dewatering and disposal
  3. Biological removal of dissolved and colloidal biodegradable organics Correct answer.
  4. Chemical precipitation of phosphorus only

Explanation

Secondary treatment is the biological stage, typically activated sludge or trickling filters, which removes dissolved and colloidal biodegradable organic matter. Preliminary and primary stages handle coarse solids and settleable matter.

Question 41Water Quality Management

A conventional activated sludge plant shows a sudden rise in sludge volume index (SVI) to over 250 mL/g with poor settling. The most likely cause is:

  1. Filamentous bulking Correct answer.
  2. Increased aeration intensity
  3. Reduced sludge age
  4. Higher dissolved oxygen

Explanation

A high SVI with poor compaction is the classic signature of filamentous bulking, where filamentous organisms bridge flocs and prevent settling. Low dissolved oxygen, nutrient imbalance or high readily biodegradable substrate often drive it.

Question 42Water Quality Management

In an activated sludge system, the food-to-microorganism (F/M) ratio is calculated as:

  1. Sludge return flow divided by influent flow
  2. Aeration tank volume divided by influent flow
  3. Mass of substrate applied per day divided by mass of microorganisms in the aeration tank Correct answer.
  4. Mass of microorganisms divided by daily substrate load

Explanation

F/M is the daily substrate load divided by the microbial mass held in the aeration tank, usually expressed as kg BOD per kg MLSS per day. It governs sludge production, oxygen demand and settling behaviour.

Question 43Water Quality Management

Effluent from a secondary plant has BOD 20 mg/L and suspended solids 30 mg/L. The total BOD of the sample after accounting for the BOD exerted by the suspended solids is best described as:

  1. Equal to the filtered BOD
  2. Higher than the filtered BOD Correct answer.
  3. Lower than the filtered BOD
  4. Independent of suspended solids

Explanation

Suspended solids in the effluent exert an additional oxygen demand as they are degraded, so the unfiltered BOD exceeds the filtered or soluble BOD. This is why effluent standards often specify both BOD and suspended solids limits.

Question 44Water Quality Management

Which process is primarily responsible for nitrogen removal in a sequencing batch reactor operating with alternating aerobic and anoxic phases?

  1. Nitrification followed by denitrification Correct answer.
  2. Coagulation and flocculation
  3. Activated carbon adsorption
  4. Phosphorus precipitation by alum

Explanation

Alternating aerobic and anoxic phases allow ammonia to be oxidised to nitrate under aerobic conditions and then reduced to nitrogen gas under anoxic conditions, achieving biological nitrogen removal. The other options address phosphorus, turbidity or trace organics rather than nitrogen.

Question 45Water Quality Management

Eutrophication of a lake is most directly driven by which nutrient combination?

  1. Sodium and potassium
  2. Calcium and magnesium
  3. Nitrogen and phosphorus Correct answer.
  4. Silica and iron

Explanation

Excess nitrogen and phosphorus stimulate algal growth, leading to blooms, oxygen depletion and taste and odour problems. Phosphorus is often the limiting nutrient in freshwater systems, while nitrogen can limit in some coastal waters.

Question 46Water Quality Management

A lake is stratified with a warm epilimnion and a cold hypolimnion during summer. The hypolimnion typically shows:

  1. Uniform oxygen throughout the depth
  2. Increased oxygen from photosynthesis
  3. Higher dissolved oxygen than the epilimnion
  4. Lower dissolved oxygen due to restricted reaeration Correct answer.

Explanation

Thermal stratification isolates the hypolimnion from atmospheric reaeration and from the photosynthetic zone, so oxygen is consumed by decomposition without replenishment. This can lead to anoxic conditions and internal nutrient release.

Question 47Water Quality Management

In lake management, the term 'internal loading' refers to:

  1. Groundwater inflow through the lake bed
  2. Pollutant inflow from tributaries
  3. Atmospheric deposition on the lake surface
  4. Release of nutrients from bottom sediments Correct answer.

Explanation

Internal loading is the release of nutrients, especially phosphorus, from bottom sediments under low oxygen or high pH conditions. It can sustain eutrophication even after external inputs are controlled.

Question 48Water Quality Management

The principal health concern with nitrate in drinking water is:

  1. Dental fluorosis
  2. Arsenicosis
  3. Skeletal fluorosis
  4. Methaemoglobinaemia in infants Correct answer.

Explanation

High nitrate converts to nitrite in the infant gut, oxidising haemoglobin to methaemoglobin and impairing oxygen transport, a condition called blue baby syndrome. The drinking water standard is set to protect this sensitive group.

Question 49Water Quality Management

Chronic exposure to arsenic above the permissible limit in drinking water is most strongly associated with:

  1. Hypertension caused by excess calcium
  2. Skin lesions and increased cancer risk Correct answer.
  3. Blue baby syndrome
  4. Dental caries

Explanation

Long-term arsenic ingestion causes characteristic skin pigmentation and keratosis and raises the risk of skin, bladder and lung cancer. Blue baby syndrome is linked to nitrate, and dental caries to fluoride deficiency.

Question 50Water Quality Management

A water sample has a pH of 8.5 and a total alkalinity of 200 mg/L as CaCO3. The bicarbonate concentration is approximately:

  1. 244 mg/L as HCO3 Correct answer.
  2. 200 mg/L as HCO3
  3. 122 mg/L as HCO3
  4. 100 mg/L as HCO3

Explanation

At pH 8.5, alkalinity is predominantly bicarbonate, and converting from CaCO3 equivalents to bicarbonate uses the ratio of 61 to 50, giving about 244 mg/L. The other values reflect incorrect molar conversions or ignoring the equivalent weight ratio.