Your Answer : (Not Answered)

Correct Answer : A

The pulp and paper waste is Black liquor.

In kraft pulping, wood chips are cooked in white liquor (sodium hydroxide and sodium sulphide) to dissolve the lignin that binds the fibres. The spent cooking liquor, dark with dissolved lignin, is black liquor. It is the industry's main waste stream and is usually concentrated and burnt in a recovery boiler to regain chemicals and energy.

Spentwash is the effluent of molasses-based distilleries, and filter cake (press mud) is a residue of sugar mills. Since neither belongs to the paper industry, 'All of the above' is wrong.

Your Answer : (Not Answered)

Correct Answer : A

Influenza, measles and mumps are air-borne infections.

All three are viral diseases spread by droplets and aerosols released when an infected person coughs, sneezes or talks, and inhaled by others nearby. That is why they spread fastest in crowded indoor places and why measles, in particular, is highly contagious.

Water-borne infections include cholera, typhoid and hepatitis A; food-borne ones include food poisoning by salmonella; and soil-borne ones include tetanus and hookworm. None of these routes is the main one for influenza, measles or mumps.

Your Answer : (Not Answered)

Correct Answer : A

The BOD limit for discharge into inland surface waters is 30 mg/L.

The general standards for discharge of environmental pollutants under the Environment (Protection) Rules, 1986 set the BOD (3 days at 27 °C) at 30 mg/L for inland surface water. The same schedule allows 350 mg/L for discharge into public sewers, which lead to a treatment plant, and 100 mg/L for land irrigation and marine coastal areas.

So 100 mg/L is the limit for land irrigation and marine discharge, not for inland surface water. 50 mg/L and 10 mg/L are not the general standard for this route.

Your Answer : (Not Answered)

Correct Answer : A

The correct matching is (a)-(3), (b)-(4), (c)-(2), (d)-(1).

• Sulphuric acid is the classic strong acid: (a)-(3).
• Potassium hydroxide (caustic potash) is a strong alkali: (b)-(4).
• Oxygen difluoride, OF₂, is a powerful oxidising and fluorinating agent: (c)-(2).
• Bromine trifluoride, BrF₃, reacts violently with water and is placed among the strong dehydrating agents in this classification: (d)-(1).

The first two pairs settle the answer, since only one code puts sulphuric acid with the acids and potassium hydroxide with the alkalis. The other codes call sulphuric acid an oxidant or an alkali, or match potassium hydroxide with dehydrating agents.

Your Answer : (Not Answered)

Correct Answer : B

The match is a-iv, b-iii, c-ii, d-i.

• Ignitable: white phosphorus, which catches fire spontaneously in air.
• Corrosive: sulphuric acid, which destroys tissue and metal.
• Carcinogenic: polyaromatic hydrocarbons, such as benzo(a)pyrene, known to cause cancer.
• Toxic: lead salts, which poison the nervous system and blood.

Sulphuric acid is the clear corrosive, and only option B pairs corrosive with it (b-iii). Options A and D call white phosphorus corrosive, and option C pairs ignitable with lead salts.

Your Answer : (Not Answered)

Correct Answer : D

The correct matching is a-iii, b-iv, c-ii, d-i.

• (a) Reacts vigorously with water: phosphorus pentoxide, which reacts violently and exothermically with water to give phosphoric acid; it is a powerful dehydrating agent.
• (b) Reacts spontaneously with air: trimethylaluminium, which is pyrophoric and ignites on contact with air.
• (c) Generates toxic fumes: aluminium nitrate, which gives off toxic nitrogen oxides when heated or in a fire.
• (d) Explosive substance: dynamite.

Option B puts trimethylaluminium against water and phosphorus pentoxide against air; trimethylaluminium does react with water too, but its defining hazard is ignition in air, and phosphorus pentoxide is not air-reactive. Options A and C pair dynamite with air or water reactivity, which misplaces the one explosive.

Your Answer : (Not Answered)

Correct Answer : B

Schedule II gives the list of waste constituents with concentration limits.

Under the Hazardous and Other Wastes (Management and Transboundary Movement) Rules, 2016, a waste is hazardous if it comes from a process listed in Schedule I, or if it contains any constituent listed in Schedule II above the concentration limit given there. Schedule II is therefore the concentration-limit test.

Schedule I is the list of processes generating hazardous waste. Schedule III lists the hazardous wastes applicable for import and export, in two parts: those requiring prior informed consent and those not requiring it. So the options about processes and about import and export describe the other schedules.

Your Answer : (Not Answered)

Correct Answer : B

Contaminated water spreads typhoid.

Typhoid is caused by Salmonella Typhi, which is shed in the faeces of infected people and carriers and is spread when sewage contaminates drinking water or food: the faecal-oral route. Safe water supply and sanitation are the main means of controlling it.

Tuberculosis and diphtheria are bacterial infections spread through the air by coughing and sneezing. Tetanus is caused by spores of Clostridium tetani from soil entering a wound; it is not spread by drinking water.

Your Answer : (Not Answered)

Correct Answer : D

Sewage-polluted water shows a high concentration of nutrients and excess growth of algae.

Sewage carries large amounts of nitrogen and phosphorus. These nutrients fertilise the water and cause algal blooms (eutrophication). When the algae die, bacteria decompose them and use up dissolved oxygen, so oxygen falls and fish may die.

The options pairing a low nutrient level with excess algae, or high nutrients with low algal growth, break the link between nutrients and algae. Low algal growth with less dissolved oxygen gets the oxygen right but not the algae, since sewage pollution stimulates algal growth rather than suppressing it.

Your Answer : (Not Answered)

Correct Answer : A

The suspended growth process is the Activated sludge process.

In a suspended growth system the microorganisms are kept floating in the wastewater as flocs, mixed and aerated in a tank. The activated sludge process works this way, and part of the settled sludge is returned to keep the microbial population high.

The other three are attached growth (fixed-film) systems, where the microbes grow as a biofilm on a surface. In a trickling filter it is the stones or plastic media over which the sewage trickles, in a rotating biological contactor it is a set of rotating discs, and in an anaerobic filter it is packing media in a closed reactor.

Your Answer : (Not Answered)

Correct Answer : A

The organisms in an oxidation pond are Bacteria and Algae.

An oxidation (stabilisation) pond works by a partnership. Bacteria, which are prokaryotes, break down the organic matter of the sewage, releasing carbon dioxide, ammonia and phosphate. Algae, which are eukaryotes, use those nutrients and sunlight for photosynthesis and release oxygen, which the bacteria need to keep oxidising the waste.

The other pairs have no prokaryote at all: mushrooms are fungi, mosses are plants, and lichens are fungus-alga partnerships. None of them is the working population of a sewage pond.

Your Answer : (Not Answered)

Correct Answer : B

Chlorination is done to remove Bacteria.

Chlorine is a disinfectant: as hypochlorous acid it penetrates and kills pathogenic bacteria and inactivates many viruses, and a small residual protects the water in the distribution pipes. It is usually the last step of treatment.

The other targets are dealt with by other steps. Hardness (calcium and magnesium) is removed by lime-soda softening or ion exchange. Sediments and suspended solids are removed by plain sedimentation, coagulation with alum and filtration, all of which come before disinfection.

Your Answer : (Not Answered)

Correct Answer : D

The correct sequence is screening → grit removal → clarification → biological treatment.

Treatment starts with preliminary steps that protect later units. Screens remove large floating objects such as rags and plastics first. Grit chambers then settle sand and gravel that would wear pumps. Primary clarification (sedimentation) removes settleable organic solids, and the clarified sewage then goes to biological (secondary) treatment such as activated sludge or trickling filters.

Grit removal before screening would let large objects damage the grit chamber, and biological treatment cannot come first. Putting biological treatment straight after grit removal leaves out primary clarification, which the standard sequence places before it.

Your Answer : (Not Answered)

Correct Answer : B

The correct matching is a-iii, b-i, c-iv, d-ii.

• (a) Stripping removes volatile compounds by passing air or steam through the waste: ethanol.
• (b) Precipitation converts dissolved toxic metals into insoluble hydroxides or sulphides that settle out.
• (c) Sorption on activated carbon removes dissolved organic solvents such as xylene.
• (d) Solvent extraction transfers oils and organochlorine compounds into an immiscible solvent.

The fastest check is precipitation, the standard method for heavy metals: only option B pairs precipitation with toxic metals. Option A pairs precipitation with oils, option C with ethanol and option D with xylene, none of which is removed by precipitation.

Your Answer : (Not Answered)

Correct Answer : D

Of the steps listed, sedimentation comes first.

Raw surface water first passes through screens and then into settling basins, where plain sedimentation lets the heavy suspended matter (sand, silt) settle under gravity. That reduces the load on everything downstream. Only then is a coagulant such as alum added, followed by flocculation and further settling, then filtration through sand beds, and finally disinfection by chlorination.

So filtration and chlorination are late stages, and coagulation follows the initial settling. The usual textbook sequence is screening, sedimentation, coagulation, filtration and disinfection, which puts sedimentation first among the four.

Your Answer : (Not Answered)

Correct Answer : C

The process is biostimulation.

Biostimulation encourages the microbes already present at a contaminated site by adding what limits them: nutrients such as nitrogen and phosphorus, and electron acceptors such as oxygen or nitrate. The native population then grows and degrades the pollutants faster.

Bioaugmentation adds new microbes, cultured strains able to degrade the pollutant, rather than stimulating native ones. Biosparging injects air below the water table and bioventing supplies air to the unsaturated zone; both deliver oxygen alone rather than nutrients and acceptors together.

Your Answer : (Not Answered)

Correct Answer : A

Asphyxiants exclude oxygen.

Simple asphyxiants are gases that are not themselves very toxic but displace oxygen from the air breathed, so that the body is starved of it. Chemical asphyxiants, such as carbon monoxide and hydrogen cyanide, prevent the body from carrying or using oxygen. Either way, it is oxygen that is kept from the tissues.

Nitrogen, carbon dioxide and methane are themselves common simple asphyxiants in confined spaces such as sewers and silos, so they are what displaces oxygen, not what is excluded.

Your Answer : (Not Answered)

Correct Answer : B

Depletion of stratospheric ozone causes skin cancer.

The ozone layer absorbs most of the sun's ultraviolet-B radiation. When it thins, more UV-B reaches the ground, and that radiation damages DNA in skin cells, raising the incidence of skin cancers, including melanoma, as well as cataracts and suppression of the immune system.

A rise in CO₂ comes from burning fuels and clearing forests, not from ozone loss. Cholera is a waterborne bacterial disease and dengue a mosquito-borne viral one; neither is caused by ultraviolet exposure.

Your Answer : (Not Answered)

Correct Answer : A

Settleable solids and floating matter are removed in primary classifiers (primary clarifiers).

In the primary sedimentation tank, sewage flows slowly enough for settleable organic solids to sink as primary sludge, while grease, oil and other floating matter rise and are skimmed off as scum. It typically removes about 50-70% of suspended solids and a quarter to a third of the BOD.

The bar screen comes first and catches large objects such as rags and plastics. The grit chamber removes heavy inorganic grit and sand, not organic settleable solids. An equalization tank evens out variations in flow and strength; it does not separate solids.

Your Answer : (Not Answered)

Correct Answer : A

Fluoride in water mainly affects the teeth.

Small amounts of fluoride (around 1 mg/L) protect teeth against decay, but above about 1.5 mg/L, the BIS limit for drinking water, it causes dental fluorosis: mottled, chalky or brown-stained enamel. Long exposure to higher levels causes skeletal fluorosis, with stiff joints and bone deformities, a problem in parts of Rajasthan, Andhra Pradesh and other states.

The brain, muscles and kidneys are not the main targets. Kidney damage is more typical of cadmium, and nervous system damage of lead and mercury.