Chapter 5: Air
Descriptive Questions
- Q: Name the main components of air?
- A: Air contains 78 percent nitrogen, 21 percent oxygen and 1 percent consists of argon, carbon dioxide and other gases. Along with these, it has water vapour, smoke and dust particles.
- Q: Write any four factors that pollute the air.
- A: The burning of fuels and gases released by automobiles, factories and industries release smoke and harmful gases into the air, which degrade the quality of the air.
- Q: State the harmful effects of ultraviolet rays.
- A: Ultraviolet rays from the sun can cause skin cancer and damage eyes.
- Q: Define air pollution.
- A: Air pollution is the contamination of air due to addition of unwanted substance.
- Q: List the properties of air.
- A: Air has weight, occupies space, exerts pressure, and is needed for burning.
- Q: What is atmosphere?
- A: A blanket of air that surrounds the Earth. It is divided into five layers: Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere.
- Troposphere: The first layer above the earth surface (12 to 18 km). Clouds are formed here.
- Stratosphere: Second layer (up to 50 km). Contains the ozone layer which absorbs harmful ultraviolet radiation. Jets fly here.
- Mesosphere: Third layer (up to 90 km). Prevents meteoroids from entering.
- Thermosphere: Fourth layer (up to 80-800 km). Space shuttles orbit here.
- Exosphere: Fifth and uppermost layer (up to 3000 km). Beyond this is empty space.
- A: A blanket of air that surrounds the Earth. It is divided into five layers: Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere.
- Q: Explain an activity to show that air exerts pressure.
- A: Take a full glass filled with water till the brim and cover the mouth of the glass with a cardboard. Press the cardboard with one hand and turn the glass upside down quickly, then remove your hands. The cardboard will not fall down and the water does not pour out because the air exerts pressure in the upward direction.
- Q: Describe the composition of air.
- A: Air consists of 78% Nitrogen, 21% Oxygen, 0.04% Carbon dioxide and other gases. Nitrogen is the most abundant gas. Oxygen is most important for living things and burning. Carbon dioxide is used by plants for photosynthesis and in fire extinguishers. Argon is used in electric bulbs and neon in glow signs. Water vapour helps in the formation of clouds.
Objective Questions
- Match the following:
- First layer of atmosphere —————–>Troposphere;
- Second layer of atmosphere ————-> Stratosphere;
- Layer extended up to 50-90 km ———->Mesosphere;
- Fifth layer of atmosphere ————–> Exosphere;
- Radio waves are transmitted ———–> Ionosphere.
- Fill in the blanks:
- The two main gases present in the air are nitrogen and oxygen.
- Living things use oxygen gas for breathing.
- Plants use carbon dioxide gas to prepare their food.
- Clouds are formed in the troposphere layer.
- Stratosphere (ozone) layer protects us from the harmful rays of the sun.
- Choose the correct option:
- The layer of the atmosphere where the space shuttles orbit is the thermosphere. ( Stratosphere / Thermosphere )
- The atmosphere extends up to many kilometres. (Kilometer / meter )
- Air ( Air / water ) is present all around but we cannot see it.
- The layer of air surrounding the earth is atmosphere. ( atmosphere / galaxy )
- True or False:
- Air is colourless, odourless and tasteless: True
- Air gets polluted due to the presence of nitrogen gas: False
- Nitrogen is required for burning: False
- Air is a mixture of several gases: True
- Answer in one word:
- Lowest layer of the earth’s atmosphere: Troposphere
- Gas essential for burning: Oxygen
- Gas abundant in the atmosphere: Nitrogen
- The outermost layer of the atmosphere: Exosphere