Class 8 Science Question Answers - Pollution of Air and Water (Old Syllabus)

Q23: Explain global warming.

Ans: The greenhouse effect is the process which leads to increase in average earth's temperature. That is the global warming. It results because of the greenhouse gases like water vapour, carbon dioxide, nitrous oxide, and methane, trap energy from the sun. When solar radiation reaches earth some of these radiations are absorbed by earth and rest are released back to the atmosphere. Greenhouse gases trap these radiations and do not allow them to go back. This helps in keeping earth warm and in survival of human beings. However an increase in amount of greenhouse gases can lead to excessive increase in earth's temperature leading to global warming.
Q24: Describe the threat to the beauty of Taj Mahal.

Ans: The major threat the beauty of Taj Mahal is the- "acid rain". When acid rain falls on the monument that is made up of marble they react with marble to form a powder like substance that gets washed away by the rain, this phenomenon is known as marble cancer.
Q25: Explain some of the air pollutants.

Ans: Water pollutants refer to contaminants that enter a waterway from a single, identifiable source, such as a pipe or ditch. Examples of sources in this category include discharges from a sewage treatment plant, a factory, or a city storm drain, that altogether makes water unfit for drinking of human beings.
Q26: Differentiate between deforestation and van Mahotsav?

Ans: Deforestation refers to the removal of forest or stands of trees, but van Mahotsav is an annual pan-Indian tree planting festival, occupying a week in the month of July, during this week lakhs of trees are planted.
Q27: What are the respiratory disorders caused by air pollution?

Ans: Asthma: Asthma is a disorder that causes the airways of the lungs to swell and narrow, leading to wheezing, shortness of breath, chest tightness, and coughing.

Chronic obstructive pulmonary disease (COPD), also known as chronic obstructive lung disease is a progressive disease that makes it hard to breathe.

Emphysema is a long-term, progressive disease of the lungs that primarily causes shortness of breath.

Bronchitis is inflammation of the mucous membranes of the bronchi, the airways that carry airflow from the trachea into the lungs.
Q28: List some of the sources of air pollutions

Ans: Smoke released from the vehicles, dust and gases like carbon monoxide, carbon dioxide, nitrogen oxides and smokes that are released by industries and by burning of fossil fuels are the major air pollutants.
Q29: How chlorofluorocarbon is harmful to us?

Ans: Chlorofluorocarbons damage the ozone layer of atmosphere which protects us from harmful ultra violet radiation of sun.
Q30: How smog is harmful to us?

Ans: Smog causes breathing difficulties like asthma and cough in human beings and wheezing in children.
Q31: What do you mean by marble cancer?

Ans: When acid rain falls on the monument that is made up of marble they react with marble to form a powder like substance that gets washed away by the rain, this phenomenon is known as marble cancer.
Q32: Write short notes on greenhouse gases.

Ans: Greenhouse gases are, sulphur dioxide carbon dioxide, nitrous oxide, and methane. These are the gas in the atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapour, carbon dioxide, methane, nitrous oxide, and ozone. Atmospheric concentrations of greenhouse gases are determined by the balance between sources (emissions of the gas from human activities and natural systems) and sinks (the removal of the gas from the atmosphere by conversion to a different chemical compound.

Q. 33. What do you mean by air pollution?
 Ans. When air is contaminated by unwanted substances which have a harmful effect on both living and non-living things, it is referred to as air pollution.

Q. 34. Name the pollutants produced by vehicles.
Ans. Vehicles produce high levels of pollutants like carbon monoxide, carbon dioxide, nitrogen oxide and smoke.

Q. 35. What is smog?
Ans. A thick fog like layer in the atmosphere, especially during winters is known as smog.

Q. 36. What is acid rain?
 Ans. Sulphur dioxide and nitrogen dioxide react with water vapour and form sulphuric acid and nitric acid. This acid drops down with rain, making the rain acidic. This is called acid rain.
Q. 37. What do you mean by Marble cancer?
Ans. Acid rain corrodes the marble of monuments. This phenomenon is called Marble cancer.

Q. 38. Write full form of CNG and LPG.
Ans. CNG - Compressed Natural Gas LPG - Liquefied Petroleum Gas
Q. 39. What is Greenhouse effect?
Ans. The reflected sun rays are trapped by the earth atmosphere. The trapped radiation warms the earth. It also warms the green house. This is called Greenhouse effect.
Q. 40. Describe global warming.
Ans. The increasing population and human activities cause the increase in  the carbon dioxide in the atmosphere. CO₂ is a warm gas, which increases the temperature of the earth’s atmosphere. This is called global warming.

Q. 41. Write some effects of global warming.
 Ans. The Following are the effects of global warming:
(i) It affects the green house.
(ii) The Gangotri glacier in the Himalayas has started melting.
(iii) It causes flood on earth.
(iv) It increases the temperature in the atmosphere.

Q. 42. What is water pollution?
Ans. The mixing of harmful substances such as sewage, toxic, chemicals, salt, etc. with water is called water pollution.

Q. 43. Write the causes of air pollution.
 Ans. Causes of air pollution:
(i) Emitting smoke by forest fire.
(ii) Poisonous gases expelled by the various industries.
(iii) Poisonous gases emitted by vehicles.
(iv) Smoke and dust arising due to human activities.

Q. 44. How is acid rain caused?
Ans. Different industries produce sulphur dioxide and nitrogen dioxide. Those gases react with water vapour and form sulphuric acid and nitric acids. These acids fall on earth with rain and cause acid rain.

Q. 45. What is ozone? How is it helpful for our environment?
Ans. Ozone is a layer of gases around the earth. It is tri-atom of oxygen atom. It protects the earth from the ultraviolet rays of the sun. The ultraviolet rays cause many disease and damage to our earth. Thus ozone layer is helpful for our environment.

Q. 46. How does water get polluted?
Ans. Water gets polluted when unwanted and harmful chemical substances are added to the water. Untreated sewage and garbage is added to water resources to pollute water.