INTRODUCTION
The contamination of environment with harmful (toxic and poisonous) substances due to the certain natural phenomena and human activities is called environmental pollution or simply as pollution.
Any substance that cause pollution is called a pollutant. A substance becomes pollutant when its concentration increases beyond a certain permissible limit in the environment.
Pollutants may belong to any of the following classes.
(A) Gaseous Pollutants : Such as Carbon monoxide, Oxides of Sulphur and Nitrogen, Chlorine gas etc.
(B) Particulate Pollutants : Such as Dust, Smoke, Fumes, Mist, Fly ash, Pesticides, Insecticides, Cement dust, etc.
AIR POLLUTION
Our atmosphere contains many gases. Some of these gases are necessary for the existance of life on the earth. Due to urbanization and industrialization, many harmful compounds are released by the factories into the atmosphere. The presence of such undesirable substances in the air makes it unfit for breathing and is called as air pollution. Thus, the contamination of air with harmful toxic gases, smoke and dust, etc., is called air pollution.
The substance which cause pollution of the air are called air pollutants. Major air pollutants are:
(i) Carbon monoxide (ii) Carbon dioxide (iii) Sulphur dioxide
(iv) Nitrogen oxides (v) Smoke (vi) Dust
Burning of Fossil Fuels
The pollutants released during the burning of these fossil fuels are:
All these pollutants released during the burning of fossil fuels cause air pollution. So, burning of fossil fuels causes air pollution.
Sources of Air Pollution
Air gets polluted due to various human activities as summarized below.
(i) Burning/combustion of fuel: Burning of fuel for household purposes generates gases like carbon dioxide, carbon monoxide as well as soot and particulate matter.
(ii) Vehicular emission: Gases emitted from the exhausts of motor vehicles contribute significantly to air pollution. These gases are nitrogen oxides, sulphur dioxide, carbon monoxide, carbon dioxide, hydrogen sulphide, etc.
(iii) Industrial emission: With the increase in population, the number of industries is increasing day by day. they emit harmful gases and smoke. For example, operations like mining of coal release coal dust into the atmosphere.
(iv) Emmissions from power plants: Thermal power plants and nuclear power plants release harmful gases, smoke and radioactive pollutants.
(v) Deforestation: Trees absorb substantial amount of carbon dioxide from the atmosphere. Hence, cutting of trees pullutes the environment by increasing the amount of carbon dioxide in the atmosphere.
(vi) Use of chlorofluorocarbons (CFCs) in refrigerators, fire extinguishers, aerosol sprays, etc. leads to release of harmful gases that deplete the ozone layer.
Effects of Air Pollution
The harmful effects of some air pollutants on living and non-living things.
* Global Warming: Increase in the concentration of carbon dioxide in the air is one of the major causes of global warming.
The trapping of the sun's radiation by the gases present in the earth's atmosphere is called greenhouse effect.
When the concentration of greenhouse gases CO2 and methane increases in the atmosphere, they trap more heat. As a result, the earth's temperature increases leading to global warming. Thus, global warming can be defined as the increase in average temeprature of the earth's atmosphere that causes corresponding changes in climate.
The causes of global warming are
(i) deforestation
(ii) burning of fossil fuels
(iii) biological degradation of organic matter present in sewage which release methane gas.
* Effects of Global Warming:
Increase in the earth's surface temeprature
Melting of glaciers and polar ice caps
Rise in the sea level which will lead to flooding of low lying and coastal areas
* Acid Rain: The oxides of sulphur and nitrogen present in the air react with water vapour and form sulphuric acid and nitric acid respectively. These acids come down with the rain making the rainwater significantly acidic. Such rain is called acid rain.
Effects of Acid Rain: Acid rain is quite corrosive and affect both living and non-living things adversely as stated below:
(i) Acid rain slowly erodes the cement, limestone and marble of buildings and corrodes steel and other metals. eg. erosion of the marble of Taj Mahal.
(ii) It destroys vegetation due to acidification of soil and accelerates leaching.
(iii) It acidifies the water of lakes and ponds and affects the survival of aquatic plants and animals.
* Depletion of Ozone Layer: The CFCs released by (refrigerators, air conditioners, sprays, etc.) in the atmosphere convert ozone into oxygen. This reduces the amount of ozone in the ozone layer and creates a hole in it.
The depletion of ozone layer affects the health of animals and human beings who are now exposed to a higher level of UV radiation. They may develop skin cancer and eye problems if exposed to these rays for prolonged period. Exposure to UV rays affects the crops also adversely.
* Prevention of Air Pollution:
(i) Use modified automobile engines where complete combustion of fuel takes place. Get exhaust gases checked regularly.
(ii) Use less polluting fuels like unleaded petrol and CNG (Compressed Natural Gas) to keep the air clean.
(iii) We should use alternative sources of energy like solar energy, hydropower, tidal energy, nuclear energy, etc. instead of fossil fuels to meet our energy requirements.
(iv) Planting as many trees as possible in the surroundings helps to clean the air.
* Affect of Air Pollutants : Pollutants in the air cause many diseases and reactions in human beings.
WATER POLLUTION
For big cities, rivers or lakes are the source of water. In the last few decades, the quality of water in many rivers and lakes has deteriorated and has become unfit for human consumption. This is called water pollution.
The main reasons for the pollution of water in our rivers and lakes are :
(i) discharge of untreated domestic sewage into rivers and lakes.
(ii) discharge of toxic industrial wastes into rivers and lakes.
(iii) excessive use of fertilizers and pesticides in agriculture.
(iv) contamination of water-bodies with toxic metals such as, lead, arsenic, cadmium, mercury, nickel etc.
The presence of pollutants such as acids, alkalies, dyes etc. make the water coloured, foul-smelling, and bad in taste.
Impact of water Pollution on the living organism :
Harmful Effect of Water Pollution
Water is an integral part of all living organisms. So, any contamination in water will affect all living organisms. For example,
(i) Polluted water can cause many diseases like cholera, dysentery, typhoid, gastroentritis, hepatitis (jaundice), diarrhoea, and skin diseases in human beings.
(ii) Contamination of rivers, lakes etc., with heavy metals like lead, mercury, copper, nickel etc., can harm both aquatic animals and human beings.
Washing away of the residual fertilizers into water-bodies by drain causes faster growth of weeds. These weeds consume most of the dissolved oxygen from the water of such water-bodies. The deficiency of oxygen in the water may cause death of aquatic animals. This loss of dissolved oxygen from water in water-bodies is called "eutrophication".
Such weeds also block sunlight and prevent the growth of aquatic plants.
Prevention of Water Pollution
Water pollution can be prevented or reduced by following the suggestions given below :
(i) Do not throw the garbage into rivers/lakes. The rivers/lakes should be cleaned from time to time.
(ii) Trees and plants must be planted along the banks of rivers.
(iii) Toxic industrial waste should be treated chemically to remove the harmful substances present in it. Only the treated waste should be discharged into rivers/lakes.
(iv) The city sewage should be treated at the sewage treatment plant to remove all suspended impurities and organic matter before discharging it into water.
(v) Excessive use of fertilizers and pesticides should be discouraged.
(vi) The use of synthetic detergents should be minimised. If possible use biodegradable detergents.
(vii) We should not wash clothes, clean utensils and take bath near the source of water.
(viii) Put a covering on the well.
Drinking Water or Potable Water – Water which is suitable for drinking is called potable water.
Drinking water should be --->
(i) colourless, transparent odourless
(ii) It should also be free from any suspended impurities, any harmful germs large quantity of salts, any harmful salt such as nitrates, cyanides, urea etc.
Water Treatment for City Supply
Water from natural sources contain many impurities. To make it fit for drinking, these impurities must be removed. The method used for purifying water depends upon the source of water. People in big cities get purified river or lake water through a network of water pipelines.
(i) Removal of suspended impurities : Water is pumped from a river or a lake into a large tank. Here, it is mixed with a small quantity of alum and allowed to stand for some time. The suspended particles of clay etc., settle down slowly at the bottom of the tank. The upper layer of water is then sent for filtration.
(ii) Filtration : The water after sedimentation is filtered through thick layers of sand and gravel. Here, the fine suspended impurities get removed.
(iii) Aeration : Air under pressure is then blown into the filtered water. This process called aeration, kills harmful microorganisms present in the filtered water.
(iv) Chlorination : The filtered and aerated water is chlorinated by adding chlorine to it. Chlorine kills all harmful germs. Thus, chlorination of water is done to make if free from all harmful microorganisms.
The purified and chlorinated water is supplied to the users through a network of water pipes.
A flowsheet diagram showing various steps for the purification of river/lake water and its supply to the users is shown below.
Purification of Water at Home
In villages and small towns, public water supply is not available. People in such places, get their water from wells, handpumps, springs or from rivers and lakes. Water from these sources may not be fit for drinking and cooking.
Small quantitiy of such water can be made fit for drinking and cooking as described below
(i) By filtration : Any suspended impurities in the water from well, river or lake can be removed by filtering water through a fine muslin cloth.
(ii) By boiling : The filtered water can be made germ-free by boiling for 10-15 minutes and cooling it before use.
(iii) By treating with some chemicals : The filtered water can also be made germ-free by adding a small quantity of any of the chemicals, such as potassium permanganate, bleaching powder or chlorine tablets.
(iv) By exposing water to ultraviolet radiation : The filtered water can also be made germ-free by exposing it to ultraviolet radiation. Now-a-days, many water-purifiers available in market are based on this method.
At domestic level, water can be purified by filtering it through the layers of gravel, sand and char-coal and boiling it before use.
SOIL POLLUTION AND EROSION
The soil is one of the major resources for the sustenance of life on the earth. However, it is often being abused by the humans. The cutting down of forests whether for agriculture, construction of buildings, roads and dams often leads to soil erosion. The excessive use of chemical fertilisers and disposal of waste materials pollutes the soil. The floods and overgrazing by animals also result in erosion of nutrient materials from the soil, making it infertile and unproductive.
The erosion of soil is a natural process, which is as old as the earth itself. Erosion involves the movement of soil from one place to another. It may be due to flowing water (flood) or wind. Nowadays, the rate of soil erosion is very high due to increase in activities of humans. As a result, the rate of soil erosion has exceeded the rate of its formation in nature. Soil erosion is a matter of global concern as it is a matter of global concern as it is destroying our resource base very rapidly.
Loss of top soil in relation to total land area is high in our country. The rate of this loss is higher in regions with high population density, mainly due to increase in the agricultural activities. Continuous cultivation of land by only one type of crop further adds to the loss of soil fertility. Once the top soil (about 20 cm thick) is lost, the sub-soil becomes a part of the layer for cultivation. This layer has less nutrient retention power, organic matter and aeration. The soil, as a living organic system, gets disturbed due to this, which in turn has a negative impact on the soil fertility and crop productivity. Deforestation, floods and overgrazing are some other main causes for the erosion of soil. You know that chemical fertilisers contain elements, like nitrogen, phosphorus, potassium, zinc and magnesium. The excess of these elements in the soil changes its composition.
The forest fires and even deep ploughing of land for crops also lead to soil erosion. You know that the water and wind take away the top layer of the soil where there is no vegetation or poor vegetation. The trees, grasses and hedges hold the soil in place.
QUICK REVISION
* Water pollution is the contamination of water by unwanted and harmful substances such as sewage, toxic chemical and industrial wastes.
* Excessive growth of algae in the waterbodies is called eutrophication.
* Major causes of water pollution are the discharge of industrial toxic wastes and untreated sewage into the river.
* Accumulation of harmful chemicals in the body of living organisms is called bioconcentration.
* Potable water is one which is suitable for drinking.
* Potable water should be colourless, odourless and free from suspended impurities, chemicals and germs.
* Water can be made fit for drinking at home, either by boiling or by using chlorine tables. Candle water filters or modern water purifiers can also be used.
* City water can be purified by sedimentation, filtration and chlorination processes.
* Cholera, typhoid, dysentery and diarrhoea are water-borne diseases.
* Pollution is induction of certain unwanted substances in air, water and land, which cause undesirable changes in properties of the air, water and land.
* A pollutant need not be harmful in itself, but in high concentrations it has harmful effects.
* Acid rain occurs when sulphur dioxide and nitrogen oxides from the burning of fossil fuels combine with water vapour in the atmosphere.
* Water pollution is the induction of objectionable matter in water that changes its properties and makes it unfit for various purposes.
* Air is a mixture of many gases, present in a fixed ratio. When the ratio is disturbed for any reason, the air is said to be polluted.
* The runoff containing chemicals and other materials used on watershed agricultural lands contributes to chemical contamination of water.
* The contamination of soil may be due to the discharge from industrial sites or leaking underground storage tanks is also a cause of pollution.
* Concentrations of nitrate in water have carcinogenic effects, which may lead to Blue Baby Syndrome, Met haemoglobin anaemia and hampering oxygen transport in blood.
* Eutrophication is the gradual increase in the concentration of phosphorus, nitrogen and other plant nutrients in an aquatic ecosystem.
* Sufficient good quality of water to be severd as drinking water is termed potable water.
IMPORTANT POINTS
* Air pollution : Contamination of air with harmful gases, dust, smoke, etc.
* Pollutant : Any harmful substance which causes pollution.
* SPM : Suspended particulate matter in the air.
* Acid rain : Rain water mixed with pollutants like oxides of sulphur and nitrogen.
* Water pollution : Contamination of water with harmful toxic substances.
* Eutrophication : Excessive growth of algae in waterbodies.
* Bioconcentration : Accumulation of harmful pesticides in the body of living organisms.
* Sedimentation : The process of settling down of suspended impurities as sediments in water.
* Chlorination : Process of adding chlorine in water to kill harmful germs.
* Potable water : Water which is fit for drinking.
* Adsorption : Absorption from surface.
ª Algal bloom : Excessive growth of algae in a water body due to contamination.
* Fluorosis : Disease caused due to consumption of fluoride rich water.
* Indoor pollution : Pollution due to indoor air.
* Non-point source : The diffuse discharges whose location cannot be identified.
* Point Sources : Readily identified single location of causing pollution.
EXERCISE - I
Q.1 ............... is a gaseous pollutant.
Q.2 DDT is a ......... Pollutant.
Q.3 Particles of dust, cement and carbon particles in smoke may cause ..........
Q.4 Air pollution can be reduced by using ...... in place of wood, coal etc.
Q.5 Major source of water pollution is ........
Q.6 ........... is added to the filtered river water to kill harmful germs present in it.
Q.7 The technique used for replenshing the ground water is called ..............
Q.8 Drinking water should be .......... and ......
Q.9 How are the pollutants classified ? Give one example of each type.
Q.10 Name various air pollutants and their sources.
Q.11 Suggest a few methods to prevent / control air pollution.
Q.12 Define 'Eutrophication'?
Q.13 How is radiactive pollution harmful to us?
Q.14 What causes acid rain?
Q.15 What types of pollutants are given off by forest fires?
Q.16 When do you call a substance a pollutant?
Q.17 Explain how fertilisers lead to contamination of water.
Q.18 How does contaminated water affect human beings?
Q.19 If water is apparently crystal clear, does that mean it is pure? Discuss.
Q.20 What are the various activities of human beings that make the air impure?
Q.21 How are plants affected by air pollution?
Q.22 How do water bodies get polluted ? List any three causes.
Q.23 How does water pollution affect marine animals?
Q.24 What steps can we take to control pollution of water bodies ?
Q.25 Discuss the three main processes employed in purification plants to make water fit for drinking.
Q.26 What do you mean by the term potable water? What are the characteristics of potable water?
Q.27 If you feel that the water supplied to your home contains germs or microorganisms, what steps can you take to make it fit for drinking ?
Q.28 Which is the major source of air pollution in metro cities?
Q.29 What are greenhouse gases?
Q.30 How Taj Mahal's beauty is in danger.
Q.31 What is the cause of global warming?
Q.32 Name the plan launched to clean the river Ganga.
EXERCISE - II
Q.1 Where was the painful bone disease Itai-itai reported first –
(A) Britain (B) India
(C) Japan (D) USA
Q.2 Which one of the following is not a green house gas –
(A) CO2 (B) CH4
(C) O2 (D) CFCs
Q.3 Montreal protocol was signed in –
(A) 1978 (B) 1987
(C) 1991 (D) 1993
Q.4 Photo chemical smog was first observed in –
(A) Los Angeles (B) Tokyo
(C) Newyork (D) Sydney
Q.5 Acid rain is due to –
(A) Water pollution
(B) Air pollution
(C) Automobile pollution
(D) Pesticide pollution
Q.6 Maximum air pollution is at –
(A) Delhi (B) Bhopal
(C) Kolkata (D) Bangalore
Q.7 Waldsterben is –
(A) Decline in forest
(B) Development of fog
(C) Harm to sculptures, statues and building (D) All of the above
Q.8 In air pollution Delhi ranks –
(A) First most polluted
(B) Second most polluted
(C) Third most polluted
(D) Fourth most polluted
Q.9 The term green house effect was given by –
(A) Fourier (B) Tyndall
(C) Arrhenius (D) Linnaeus
Q.10 The term 'acid rain' was given by –
(A) Fourier (B) Augus
(C) Tyndall (D) Linnaeus
Q.11 Chlorination of treated waste water is required for –
(A) Killing all mircobes
(B) Removing suspended materials
(C) Complete breakdown of organic matter (D) All of the above
Q.12 Black foot disease in humans is caused by –
(A) Arsenic (B) SPM
(C) Fluorine (D) Cadmium
Q.13 Ozone depletion shall cause higher incidence of –
(A) Skin cancers (B) Cataract
(C) Decreased immunity
(D) All of the above
Q.14 Eutrophication of water body occur due to addition of
(A) Detergents (B) Fertilisers
(C) Sewage (D) All of the above
Q.15 Minamata disease is due to pollution of
(A) Organic waste into drinking water (B) Oil spill in water
(C) Industrial waste mercury into fishing water (D) Arsenic into the atmosphere
Q.16 DDT is –
(A) Green house gas
(B) Degradable pollutant
(C) Nondegradable pollutant
(D) None of these
National environmental engineering research institute is at –
Q.17 (A) Kanpur (B) Nagpur
(C) Delhi (D) Madras
Q.18 The most polluted city of the world is –
(A) Newyork (B) Tokyo
(C) Mexico (D) Kolkata
Q.19 Green house effect is mostly due to –
(A) H2 (B) CO
(C) CO2 (D) N2
Q.20 Unleaded petrol has been introduced in India with effect from –
(A) First January 1996
(B) First April 1995
(C) First April 1996
(D) First January 1997
ANSWERS KEYS
1. C 2. C 3. B 4. A
5. B 6. A 7. A 8.
D 9. C 10. B 11. A 12. A
13. D 14. D 15. C 16. C
17. B 18. B 19. C 20. B
EXERCISE - III
1. The pie chart shows the composition of air. Identify the gases W, X, Y and Z -
W X Y
(A) Nitrogen Rare gases Oxygen
(B) Carbon Oxygen Rare gases
(C) Nitrogen Oxygen Rare gases
(D) Rare gases Hydrogen Oxygen
2. Which air pollutant is wrongly matched with the effect-
(A) Dust -reduces photosynthesis in green plants
(B) Carbon monoxide-reduced oxygen in the blood
(C) Chlorofluorocarbon -damages nerves and tissues
(D) Nicotine-hardens and narrows blood vessels
3. Which of the following does not cause air pollution-
(A) Establishing forest reserves
(B) Using pesticides in farms
(C) Developing housing estates (D) Quarrying for limestone
4. The following diseases are related to smoking except-
(A) Emphysema (B) Measles (C) High blood pressure (D) Cancer of the lungs
5. Which of the following is not due to air pollution
(A) Thinning of the ozone layer
(B) Increases in the number of diabetic patients
(C) Destruction of habitats (D) Global warming
6. Ozone consists of -
(A) Three carbon of atoms
(B) Three oxygen atoms
(C) One carbon atoms and two oxygen atoms (D) One oxygen and two hydrogen atoms
7. The gas associated with the greenhouse effect is -
(A) Carbon dioxide (B) Oxygen (C) Nitrogen (D) Sulphur
8. Which of the following is a fossil fuel-
I. Tar II. Coal III. Petroleum
(A) I only
(B) I and II only
(C) II and III only (D) I, II and III
9. Carbon particles and smoke from factories -
(A) Increases the rate of respiration in plants
(B) Decrease the rate of photosynthesis in plants
(C) Increase the absorption of carbon dioxide by plants
(D) Decrease the rate of transpiration in plants
10. ......gas cause green effect house effect-
(A) CO2 (B) CH4 (C) H2 (D) Both and b
11. Rhizobium bacteria, which converts atmoshpheric N2 into compounds of N2 is present in the root nodules of plants belonging to -
(A) Onion family (B) Grass family (C) Leguminous family (D) None of these
12. In the process of photosynthesis plants consume
(A) O2 (B) CO (C) CO2 (D) N2
13. CH4 + O2 ® ? Methane reacts with oxygen to form
(A) CO2 + 2H2O (B) CO + H2O (C) H2 + O2 +C (D) CO2 + H2
14. Atmospheric N2 fixation takes place in presence of -
(A) Rainfall (B) Windstorm (C) Lighting (D) Snowfall
15. Oxy-acetylene flame is used for -
(A) Refining metal (B) Welding metal (C) Melting metal (D) None of these
16. ............gas is used to preserve perishable food
(A) O2 (B) N2 (C) CO2 (D) None of these
17. Depletion of ozone layer takes place due to -
(A) Methyl alcohol (B) Carbon tetrachloride (C) Benzene (D) Chlorofluorocarbon
18. Carbon cycle ensures a constant .........in atmosphere-
(A) % of CO2 (B) Pressure of CO2 (C) Pressure of CO2 (D) % of CO
19. Rain water containing ............is called acid rain
(A) H2SO4 (B) HNO3 (C) HCl (D) Both and A and B
20. Carbogen contains -
(A) 95%CO2, 5% O2
(B) 5%CO2, 95% O2
(C) 5%N2, 95% O2
(D) 5% CO2, 95% N2
21. Which of the following affects nervous system-
(A) Oxides of N2
(B) CO
(C) Compound of lead (D) CO2
22. When ..........is inhaled carboxyhaemoglobin is formed -
(A) O2 (B) CO (C) N2 (D) CO2
23. All plant need nitrogen to make ...........
(A) Protein (B) Carbohydrates (C) Fats (D) Minerals
24. CO2 is ................towards litmus -
(A) Acidic (B) Basic (C) Neutral (D) Amphoteric
25. ................is used as fuel in rockets -
(A) Liquids H2 (B) Liquids N2 (C) O2 (D) Liquid O2
26. Solid ..........is called dry ice -
(A) SO2 (B) CO2 (C) N2 (D) H2O
27. CO is ...............toward litmus -
(A) Amphoteric oxide
(B) Basic
(C) Oxidic
(D) Neutral
28. Ozone is present in -
(A) Troposphere (B) Stratosphere (C) Mesosphere (D) Ionosphere
29. .............makes the burning of petrol more efficient but unhealthy-
(A) Compounds of lead
(B) Compounds of iron (C) Compounds of tin (D) Compounds of zinc
30. Air pollution can be controlled by -
(A) Reduce use of fossil fuel
(B) By filtering out the solid particles from smoke (C) Using unleaded petrol (D) By all of these
31. Carbon monoxide poisoning is most likely to occur in a -
(A) Open place with coal burning
(B) Room with L.P.G. gas burning
(C) Closed room with coal burning (D) Charcoal burning in open space
32. When one sucks through a straw, the pressure inside becomes ..........that the atmospheric pressure on the surface of liquids -
(A) More (B) Less (C) Equal to (D) None
33. ..........is the cheif source for producing nitrogenous fertilizers-
(A) O2 (B) H2O (C) NH3 (D) O3
34. Oxygen on liquification changes to -
(A) Blue liquid (B) Green liquid (C) Red liquid (D) None of these
35. The atmospheric pressure at sea level is -
(A) 76 mm height of Hg
(B) 76 cm height of Hg
(C) 7.6 cm height of Hg (D) 760 cm height of Hg
36. Oxygen can be prepared by-
(A) Heating mercuric oxide
(B) Heating potassium chlorate
(C) Heating hydrogen peroxide (D) All of these
37. ..........gas is used to fill electric bulb at low pressure -
(A) O2 (B) H2 (C) Ar (D) N2
38. The noble gas used in treatment of cancer is -
(A) Randon (B) Argon (C) Neon (D) Helium
39. ...........gas used for making advertising glow tubes -
(A) H2 (B) N2 (C) Ne (D) O2
40. ............is used for growing vegetable in snow bound region -
(A) Light (B) Green house effect (C) Acid rain (D) Fertiliser
41. 78% of air by volume is -
(A) Nitrogen (B) Carbon dioxide (C) Oxygen (D) Ozone
42. Due to direct exposure to sun's radiation the atoms covert into ions in -
(A) Troposphere (B) Ionosphere (C) Ozone layer (D) Stratosphere
43. Dentrifying bacteria-
(A) Converts atmospheric N2 into nitrates
(B) Converts nitrogen from the soil
(C) Converts nitrate of soil back into atmospheric nitrogen
(D) Have nothing to do with N2 cycle
44. The layer of atmospheric nearest to earth surface is -
(A) Troposphere (B) Stratosphere (C) Ozone layer (D) Ionosphere
45. Aneroid barometer means -
(A) Without liquid (B) Without solid (C) Without gas (D) Without liquid and gas
46. 0.03% of air consists of -
(A) Ar (B) N2 (C) O2 (D) CO2
47. At sea level, atmospheric pressure in equal to the weight of a mass acting on every square centrimeter-
(A) 1gm (B) 10kg (C) 1kg (D) 10gm
48. Barometer is a thin glass tube containing -
(A) Mercury (B) Lead (C) Tin (D) Tungsten
49. The layer of atmospheric which is cold, thin without cloud and dust it-
(A) Troposphere (B) Ozone layer (C) Stratosphere (D) Ionosphere
50. Atmospheric pressure .........as the attitude ........
(A) Increases, increases
(B) Decreases, decreases (C) Decreases, increases (D) Remain same
ANSWERS KEYS
1. C 2. C 3. A 4. B
5. B 6. B 7. A 8. C
9. B 10. A 11. C 12. C
13. A 14. C 15. B 16. B
17. D 18. A 19. D 20. B
21. C 22. B 23. A 24. A
25. A 26. B 27. D 28. B
29. A 30. D 31. C 32. B
33. C 34. A 35. B 36. D
37. C 38. A 39. C 40. B
41. A 42. B 43. C 44. A
45. A 46. D 47. C 48. A
49. C 50. C