JEE Chemistry Environmental Chemistry MCQs Set 11

Answer: (d) Sulphur dioxide

Explanation:
1. Fossil fuels such as coal and oil contain sulphur.
2. On burning, the sulphur forms SO\(_2\) (and some SO\(_3\)), so sulphur dioxide is the main pollutant from fossil fuels.

Teacher's Note:
1. Coal and petroleum contain sulphur compounds, which is why their combustion gives oxides of sulphur.
2. Oxides of nitrogen mainly arise from the reaction of N\(_2\) and O\(_2\) at high engine temperature.

Answer: (b) acidity

Explanation:
1. SO\(_2\) and NO\(_2\) are oxidised and react with water to give H\(_2\)SO\(_4\) and HNO\(_3\).
2. These acids raise the acidity of rain, soil and water.

Teacher's Note:
1. Oxides of non-metals such as S and N are acidic oxides.
2. Their acids fall as acid rain.

Answer: (d) combines with haemoglobin

Explanation:
1. CO binds to haemoglobin to form carboxyhaemoglobin.
2. This complex is about 300 times more stable than oxyhaemoglobin, so the oxygen-carrying capacity of blood falls.

Teacher's Note:
1. Carboxyhaemoglobin formation is the key toxic action of CO.
2. Its binding to haemoglobin is much stronger than that of oxygen.

Answer: (a) excess NO\(_2\) and SO\(_2\) from burning fossil fuels

Explanation:
1. Oxides of sulphur and nitrogen dissolve in rain water to form H\(_2\)SO\(_4\) and HNO\(_3\).
2. CO and CO\(_2\) are not responsible for acid rain, and NH\(_3\) is basic.

Teacher's Note:
1. Acid rain has pH below 5.6.
2. Normal rain is slightly acidic because of dissolved CO\(_2\).

Answer: (d) air, water and soil

Explanation:
1. DDT is sprayed into air, it settles on soil and is washed into water bodies.
2. It is non-biodegradable, so it contaminates air, water and soil.

Teacher's Note:
1. DDT persists in the environment and moves up the food chain.
2. Its use has been banned in India.

Answer: (b) chlorine

Explanation:
1. UV radiation in the stratosphere splits CFCs and releases chlorine free radicals.
2. These radicals catalytically destroy ozone.

Teacher's Note:
1. The C-Cl bond is weaker than the C-F bond, so Cl atoms are released.
2. Cl radicals are regenerated, so one atom destroys many ozone molecules.

Answer: (c) lead

Explanation:
1. Leaded petrol released lead compounds in exhaust.
2. Lead damages the development of red blood cells, kidney and the nervous system.

Teacher's Note:
1. Leaded petrol was the primary source of air-borne lead.
2. The tolerable limit of lead in drinking water is about 50 ppb.

Answer: (b) cool and humid climate

Explanation:
1. Classical smog is a mixture of smoke, fog and SO\(_2\).
2. It forms in cool, humid weather, whereas photochemical smog needs warm, dry, sunny weather.

Teacher's Note:
1. Classical smog is reducing in nature.
2. Photochemical smog is oxidising.

Answer: (d) polycyclic aromatic hydrocarbons

Explanation:
1. Benzene, toluene and nitrobenzene are volatile liquids that stay in the gas phase.
2. Polycyclic aromatic hydrocarbons are solids that are adsorbed on soot and ash particles.

Teacher's Note:
1. PAHs are carcinogenic.
2. They come from incomplete combustion of fuels.

Answer: (d) NO and O\(_3\) irritate the nose and throat, and high concentrations cause headache, chest pain, dryness of throat, cough and difficulty in breathing.

Explanation:
1. Photochemical smog is oxidising because it contains NO\(_2\), O\(_3\) and PAN.
2. It forms in warm, sunny weather, not winter, and it is not sulphurous.
3. Only the last statement is correct.

Teacher's Note:
1. Sulphurous smog means classical smog.
2. Photochemical smog needs sunlight.

Answer: (a) CH\(_4\)

Explanation:
1. Methane absorbs infrared radiation and is a greenhouse gas.
2. N\(_2\), Ar and O\(_2\) do not absorb infrared radiation appreciably.

Teacher's Note:
1. Other greenhouse gases are N\(_2\)O, O\(_3\), CFCs and water vapour.
2. Homonuclear diatomic gases do not absorb IR.

Answer: (c) Nuclear chemistry

Explanation:
1. Green chemistry uses light, ultrasound and biological catalysts to reduce hazardous waste.
2. Nuclear chemistry produces radioactive waste, so it is not part of green chemistry.

Teacher's Note:
1. Green chemistry reduces material, energy and waste.
2. It prefers water as the reaction medium.

Answer: (d) ozone

Explanation:
1. UV splits O\(_2\) into O atoms.
2. O + O\(_2\) \(\rightarrow\) O\(_3\), so ozone is formed.

Teacher's Note:
1. This is the natural formation of the ozone layer.
2. The same UV is absorbed by ozone.

Answer: (b) increased incidence of skin burns and skin cancer

Explanation:
1. Less ozone means more UV-B reaches the earth.
2. This causes sunburn, cataract and skin cancer.

Teacher's Note:
1. Ozone absorbs harmful UV radiation of about 200-315 nm.
2. The effects on skin are the main health concern.

Answer: (c) Photosynthesis

Explanation:
1. Decay, respiration and burning all release CO\(_2\).
2. Photosynthesis consumes CO\(_2\) and releases O\(_2\).

Teacher's Note:
1. Green plants keep the CO\(_2\) level balanced.
2. Deforestation upsets this balance.

Answer: (c) S1, S2 and S4 only

Explanation:
1. S1 is true: dust is a non-viable particulate.
2. S2 is true: this is the basis of the electrostatic precipitator.
3. S3 is false: O\(_2\) is not a greenhouse gas.
4. S4 is true: algae are living organisms. So S1, S2 and S4 are correct.

Teacher's Note:
1. Viable particulates are living organisms such as bacteria, fungi and algae.
2. Smoke, dust, mist and fumes are non-viable.

Answer: (c) It is beneficial because ozone cuts off the ultraviolet radiation of the sun.

Explanation:
1. Stratospheric ozone absorbs harmful UV radiation.
2. Visible light needed for photosynthesis is not blocked.

Teacher's Note:
1. Ozone is toxic near the ground but protective in the stratosphere.
2. Do not confuse the two roles.

Answer: (b) CO

Explanation:
1. Complete combustion gives CO\(_2\) and H\(_2\)O.
2. Carbon monoxide is formed only when combustion is incomplete.

Teacher's Note:
1. Water vapour forms in both complete and incomplete combustion.
2. Oxides of nitrogen form at high temperature, not through incomplete combustion.

Answer: (d) Chlorine nitrate

Explanation:
1. Chlorine nitrate ClONO\(_2\) is formed from ClO and NO\(_2\).
2. On polar stratospheric clouds it is hydrolysed to HOCl and reacts with HCl to give Cl\(_2\); sunlight then releases Cl radicals.

Teacher's Note:
1. Polar stratospheric clouds provide the surface for these reactions.
2. The ozone hole appears in spring.

Answer: (d) Troposphere

Explanation:
1. The troposphere extends from the ground to about 10 km (up to about 18 km at the equator).
2. 5 km lies inside the troposphere.

Teacher's Note:
1. Order from the ground: troposphere, stratosphere, mesosphere, thermosphere.
2. The stratosphere starts at about 10-15 km.

Answer: (c) PAN

Explanation:
1. Peroxyacetyl nitrate is formed in the atmosphere from NO\(_2\), O\(_3\) and hydrocarbons.
2. CO\(_2\), N\(_2\)O and SO\(_2\) are released directly.

Teacher's Note:
1. Secondary pollutants are formed by reactions among primary pollutants.
2. Ozone and PAN in smog are secondary pollutants.

Answer: (a) Chlorophyll

Explanation:
1. Chlorophyll drives photosynthesis.
2. Photosynthesis takes in CO\(_2\) and releases O\(_2\), keeping the balance.

Teacher's Note:
1. Chlorophyll contains magnesium.
2. Vitamin B\(_{12}\) contains cobalt.

Answer: (d) Pathogens and PCBs

Explanation:
1. Pathogens enter water from sewage and animal excreta.
2. PCBs are industrial organic pollutants. Automobile exhaust mainly pollutes air. So (1) and (3) both pollute water.

Teacher's Note:
1. PCBs are suspected carcinogens.
2. Pathogens such as E. coli cause gastrointestinal diseases.

Answer: (a) more than that of clean water

Explanation:
1. Sewage is rich in organic matter.
2. Bacteria need a lot of oxygen to decompose it, so its BOD is high.

Teacher's Note:
1. BOD below 5 ppm indicates clean water.
2. BOD of 17 ppm or more indicates highly polluted water.

Answer: (b) dissolved oxygen

Explanation:
1. Excess nutrients cause a dense algal bloom.
2. When the algae die and decay, bacteria consume the dissolved oxygen.

Teacher's Note:
1. Phosphate fertilisers are a common cause.
2. Fish die because of oxygen shortage.

Answer: (d) C\(_2\)H\(_5\)OH

Explanation:
1. BOD rises when oxidisable organic matter is present.
2. Ethanol is oxidised by bacteria using dissolved oxygen. CO\(_2\), O\(_3\) and H\(_2\)O are not oxidisable organic matter.

Teacher's Note:
1. BOD measures oxygen used by bacteria to break down organic matter.
2. Higher BOD means more pollution.

Answer: (a) microorganisms

Explanation:
1. Bacteria and other microorganisms decompose the organic matter in sewage.
2. Treatment plants also rely on microorganisms.

Teacher's Note:
1. Aerobic bacteria need dissolved oxygen.
2. Anaerobic bacteria produce foul-smelling products.

Answer: (c) Phosphate

Explanation:
1. Sodium chlorate, sodium arsenite and triazines are used to kill weeds.
2. Phosphate is a plant nutrient.

Teacher's Note:
1. Triazines are organic herbicides used in corn fields.
2. Arsenic compounds are toxic to mammals.

Answer: (b) biodegradable pollutants

Explanation:
1. Kitchen waste, leaves and food scraps decompose by microorganisms.
2. So domestic waste is mostly biodegradable.

Teacher's Note:
1. Biodegradable waste can be composted.
2. Plastics and metals should be recycled.