Chapter: 06. Air And Atmosphere
Exercise For Revision (First Section)
A. Tick (✓) the correct options.
The force that binds the layer of air to the surface of the earth is called Which of the following is not a characteristic of air? (b) It cannot be compressed. Which of the following is a component of air that supports burning? In a movie, a spaceship explodes and continues to burn as it moves through space. This cannot happen in reality because (a) space does not have oxygen B. Match the following.
Carbon dioxide - (e) 0.03 % Water vapour - (b) Variable Exercise For Revision (Second Section)
A. Tick (✓) the correct options.
Exhaled air has and than inhaled air. © more carbon dioxide, less oxygen Which of the following is not correct about respiration? (d) A large amount of heat and light is produced. Oxygen is not necessary for Which of the following fuels does/do not leave any residue on burning? (d) both (b) and © (CNG and LPG) Photosynthesis is a process in which plants take in and give out . (b) carbon dioxide, oxygen Fuels like kerosene are required to burn a piece of wood. Why does wood not burn with a matchstick in normal conditions? © Matchstick cannot heat the wood to its ignition temperature. B. Assertion-Reason based Questions.
Assertion: There is more carbon dioxide in exhaled air than inhaled air.
Reason: Plants use carbon dioxide during photosynthesis. (b) Both A and R are true but R is not the correct explanation of the assertion. Assertion: CNG is a clean fuel.
Reason: It leaves no residue on burning. (a) Both A and R are true and R is the correct explanation of the assertion. Exercise For Revision (Third Section)
A. Tick (✓) the correct options.
Which of the following is not necessary for rusting? In which of the following ways does carbon dioxide not enter the atmosphere? Which of the following are not air pollutants? Which of the following is not a cause of air pollution? Which of the following is not a harmful effect of air pollution? B. Assertion-Reason based Question.
Assertion: An iron nail left in the open rusts.
Reason: On exposure to air and moisture, paint prevents the iron from rusting. © A is true but R is false. Complete the flowchart for Revision
Other gases: Water vapour Other variable components: Dust particles EXERCISE (Chapter End Questions)
Short Answer Questions:
What is atmosphere? What would have happened if there would have been no atmosphere around the earth? The atmosphere is a thin layer or blanket of air that surrounds the Earth, held in place by gravity. If there were no atmosphere, the Earth would experience extreme temperature fluctuations (burning during the day, freezing at night), and there would be no protection from the Sun’s harmful rays, making life impossible. What is the composition of air? Air is a mixture of gases, primarily composed of Nitrogen (approx. 78%), Oxygen (approx. 21%), Carbon dioxide (approx. 0.03%), Other gases (approx. 0.93%), and variable amounts of Water vapour and Dust particles/other impurities. What is acid rain? How does it affect us? Acid rain forms when harmful gases like sulphur dioxide and nitrogen dioxide, released from burning fossil fuels, react with water vapour and oxygen in the atmosphere to create sulphuric acid and nitric acid, which then fall with rain. It damages crops, aquatic life, buildings (especially marble), and metallic objects. How is burning different from respiration? State three ways.
Give reasons:
(a) Aquatic animals and plants survive in water. Aquatic animals and plants survive in water because water contains dissolved oxygen, which they utilize for respiration.
(b) A burning candle stops burning when covered with a glass tumbler. A burning candle stops burning when covered with a glass tumbler because burning requires oxygen. The limited amount of oxygen trapped inside the glass is quickly used up, and once it’s gone, the flame extinguishes. Long Answer Questions:
List two uses each of oxygen, carbon dioxide, nitrogen and water vapour. Essential for respiration in all living organisms. Supports burning (combustion) of substances. Used by green plants for photosynthesis (making food). Used in fire extinguishers and as dry ice for cooling. Main component of proteins, essential for the growth of living organisms. Used in fertilizers to increase soil fertility. Provides moisture to plants and animals. Helps in predicting climatic conditions (humidity). What is rusting? How does it take place? Is it useful or harmful for us? Rusting is the process where iron objects develop a reddish-brown, flaky substance (rust) when exposed to moist air for a few days. It takes place when iron reacts with oxygen and water (moisture). The chemical reaction is: Iron + Oxygen + Water → Hydrated iron oxide (Rust). Rusting is harmful for us because the layer of rust falls off, exposing fresh iron and continuing the process, which weakens the iron object and makes it useless. What is air pollution? Write its causes and effects? Air pollution is the contamination of air with unwanted substances that have harmful effects on both living organisms and non-living things. Increase in human population and associated activities. Cutting of forests (deforestation). Burning of fossil fuels (coal, petrol, diesel) in industries and vehicles. Emission of harmful gases from industries. Increase in the number of automobiles and their exhaust emissions. Natural events like volcanic eruptions and forest fires. Harmful Effects of Air Pollution: Causes respiratory problems (e.g., asthma), headaches, eye irritation, and chest pain in humans. Affects the rate of photosynthesis and growth in plants. Leads to environmental problems like acid rain, global warming, and ozone layer depletion. Forms smog, which reduces visibility and causes accidents. How is the balance of oxygen and carbon dioxide maintained in nature? The balance of oxygen and carbon dioxide in nature is maintained through a continuous cycle involving living organisms and plants. Living organisms (animals and plants) and the burning of fuels consume oxygen and release carbon dioxide into the atmosphere through respiration and combustion, respectively. Conversely, green plants use carbon dioxide from the air during photosynthesis to make their food and, in turn, release oxygen back into the atmosphere. This interdependent process ensures that the levels of oxygen and carbon dioxide generally remain stable and balanced in nature. Briefly describe ozone layer depletion and global warming. Ozone Layer Depletion: The ozone layer is a protective shield in the atmosphere that absorbs harmful ultraviolet (UV) radiation from the Sun. Ozone layer depletion occurs when man-made chemicals, primarily chlorofluorocarbons (CFCs), react with and break down ozone molecules. This thinning of the ozone layer allows more harmful UV radiation to reach the Earth’s surface, increasing the risk of skin diseases and cancer in humans. Global Warming: Global warming is the observed increase in the average temperature of the Earth’s atmosphere. It is caused by an enhanced greenhouse effect, where an increased concentration of greenhouse gases (like carbon dioxide, methane, nitrous oxides, and CFCs) in the atmosphere traps more heat from the Sun. These greenhouse gases are primarily released by human activities such as the burning of fossil fuels and deforestation. Application/Skill-based Questions:
Look at the picture (Fig. A) given alongside. What change do you observe in the colour of limewater? Why does this change occur? What can we conclude from this activity?
Observation: The limewater (calcium hydroxide solution) will turn milky. Reason: This change occurs because the exhaled air contains a higher concentration of carbon dioxide. When carbon dioxide reacts with limewater, it forms calcium carbonate, an insoluble white precipitate that makes the solution appear milky. Conclusion: This activity demonstrates that exhaled air contains carbon dioxide. Observe the given chart and identify the unknown substances (A, B and X) and process (Y).
Gas A: Carbon dioxide (used by plants in photosynthesis, released by respiration) Gas B: Oxygen (produced by photosynthesis, consumed by respiration) Substance X: Food/Glucose (produced by photosynthesis, consumed by humans/animals) Process Y: Respiration (consumes food/X and Oxygen/Gas B to produce Energy, Carbon dioxide/Gas A, and Water) The presence of atmosphere maintains the temperature of the earth. Increasing the amount of one of the components ‘X’ of air is responsible for the increase in temperature of the earth at an alarming rate.
(a) What is component ‘X’ here? Component ‘X’ is Carbon dioxide.
(b) What is the cause of the increase in the amount of component ‘X’? The primary causes of the increase in carbon dioxide are human activities like the burning of fossil fuels (coal, oil, natural gas) for energy in industries, vehicles, and homes, and deforestation (cutting down trees).
© How can you prevent the increase of ‘X’? We can prevent the increase of ‘X’ (carbon dioxide) by: Planting more trees (afforestation). Reducing the use of fossil fuels by switching to renewable energy sources (solar, wind). Using public transport, cycling, or walking instead of private vehicles. Improving energy efficiency in homes and industries. In summer season, there was a power cut in Jay’s village. It was very warm, and Jay was unable to sleep in his room. He came out of the house. It was breezy. Jay decided to sleep in a yard under a tree. His mother asked him not to do that. Why do you think Jay’s mother said so? Explain. Jay’s mother likely asked him not to sleep under the tree because plants, like animals, undergo respiration continuously, even at night. During respiration, plants take in oxygen and release carbon dioxide. While plants perform photosynthesis (releasing oxygen) during the day, they only respire at night. If Jay sleeps very close under a tree at night, the concentration of carbon dioxide released by the tree’s respiration could be higher in that immediate area, and the oxygen concentration slightly lower, making the air less fresh for breathing. 
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