So, the “Air and Atmosphere” chapter for Class 6 probably tells kids that the air all around us isn’t just one thing, but a mix of different gases. The big players are nitrogen (lots of it!), oxygen (the stuff we breathe), a little bit of carbon dioxide (plants love it!), and some water vapour. Plus, there’s a sprinkle of other gases and even tiny bits of dust.
Then, it talks about the atmosphere, which is like a big cozy blanket of these gases wrapped around the Earth, held there by gravity. This blanket is super important because it gives us the air we need to live and also protects us from nasty stuff out in space. They might even mention the different layers, especially the one we live in where all the weather happens, and that special layer that protects us from the sun’s harmful rays.
EXERCISE-I
Question 1.
What is the atmosphere ?
Answer:Earth’s atmosphere is indeed our life-giving, gravity-held shield. It’s the reason we’re protected from nasty radiation, enjoy a livable temperature, and have air to breathe. Plus, it’s a constantly shifting system, shaped by nature and, increasingly, by us.
Question 2.
Why can’t we see air ?
Answer:Air because its main ingredients, nitrogen and oxygen, are like perfectly clear glass. Light passes right through them without anything to catch our eye, so the air itself remains invisible to us.
Question 3.
What is wind ?
Answer:
Wind is simply air in motion. These pressure differences are often caused by the sun heating the Earth unevenly. So, in short, wind is the atmosphere’s way of evening out temperature and pressure.
Question 4.
What would have happened if there would have been no atmosphere around the earth ?
Answer:
Here’s a glimpse of what would happen:
- No air to breathe: Oxygen, essential for most life, wouldn’t exist.
- Extreme temperature swings: Without the atmosphere to trap heat, the surface would experience scorching hot days and frigid nights, much like the Moon.
- Constant meteor bombardment: The atmosphere burns up most small meteors before they reach the ground. Without this protection, impacts would be far more frequent.
- No sound: Sound waves need a medium to travel through, and in a vacuum, there would be complete silence.
- Boiling and freezing water: Without atmospheric pressure, liquid water couldn’t exist stably. It would immediately boil away into vapor in warmer areas and freeze in colder ones.
- Blue skies and vibrant sunsets would vanish: The scattering of sunlight by the atmosphere gives us blue skies and colorful sunsets. Without it, the sky would be black, even during the day, with stars visible
Question 5.
Why is air called a mixture ? Give five facts in support of your answer.
Answer:
Air is called a mixture
Here are five supporting facts:
- Variable Composition: The amounts of gases in air, like water vapor and carbon dioxide, can change.
- Physical Separation: Air’s components can be separated through physical processes, such as fractional distillation.
- Retained Properties: Each gas in air keeps its own properties; for example, oxygen still supports burning.
- No Fixed Formula: Air doesn’t have a specific chemical formula like water (H2O) does.
- Mixture Boiling Point: Liquid air doesn’t boil at one specific temperature.
Question 6.
What are the main components of air ? Write down the composition of three main gases present in air by volume.
Answer:
The air we breathe is a mixture, with nitrogen making up about 78%, oxygen around 21%, and argon close to 0.9% by volume.
Question 7.
What do you observe when
(a) Ice cold water is filled in a glass tumbler.
(b) A burning candle is covered with an inverted jar.
(c) Carbon dioxide gas is passed through lime water.
(d) A beam of light is allowed to enter a closed dark room through a small hole.
Answer:
(a) Icy Glass: See those little water beads on your cold drink? That’s the air’s humidity getting cold and turning into water droplets right on the glass.
(b) Candle in a Jar: Watch the flame shrink and die out. It’s using up all the air (specifically the oxygen) inside, and without fresh air, it can’t burn anymore.
(c) Lime Water & CO2: When you bubble that gas through clear lime water and it turns milky, that’s a telltale sign of carbon dioxide doing its thing.
(d) Light in the Dark: That’s because tiny bits of dust in the air are bouncing the light around, making the path visible. Otherwise, you wouldn’t see the beam itself.
Question 8.
Write the chemical name of –
(a) Lime water
(b) The white insoluble solid formed on reaction of carbon dioxide with lime water.
Answer:
(a) Lime water: Calcium hydroxide
(b) The white insoluble solid formed on reaction of carbon dioxide with lime water: Calcium carbonate
EXERCISE-II
Question 1.
Name two important processes supported by oxygen present in air.
Answer:
Two crucial processes supported by oxygen in the air are respiration (allowing living organisms to produce energy) and combustion (the burning of materials).
Question 2.
Give two uses of the following components present in air:
(a) oxygen
(b) nitrogen
(c) carbon dioxide
(d) water vapour
Answer:
(a) Hot oxygen is a powerhouse for industrial processes like steelmaking and welding.
(b) Nitrogen is a fundamental building block of life, crucial for our proteins, DNA, and keeping plants healthy through fertilizers.
(c) Carbon dioxide is the lifeblood of the plant world, enabling photosynthesis and indirectly fueling all food chains by releasing the oxygen we breathe.
(d) Water vapor is a key player in our climate, influencing humidity, cloud formation, and precipitation, with industrial applications in providing moisture and generating power.
Question 3.
Define the following:
(a) Respiration
(b) Photosynthesis
(c) Combustion.
Answer:
(a) Respiration: It’s the process where living organisms break down food (like glucose) to release energy, often using oxygen and releasing carbon dioxide and water as byproducts.
(b) Photosynthesis: This is how green plants and some other organisms make their own food. They use sunlight, water, and carbon dioxide to create glucose (a sugar) and release oxygen. It’s like they’re tiny solar-powered food factories.
(c) Combustion: It’s a chemical process where a substance reacts rapidly with an oxidant, usually oxygen, to produce heat and light. Think of burning wood or fuel – it’s a fast release of energy.
Question 4.
What are fuels ? Give two examples of modern fuels.
Answer:
CNG primarily comes from natural gas wells or is found alongside oil extraction. It’s natural gas compressed for easier storage and use in vehicles.
LPG is obtained during the refining of crude oil or from natural gas processing. It mainly consists of propane and butane, liquefied under pressure for transport and use in cooking, heating, and vehicles.
Question 5.
Give reasons :
(a) Aquatic animals and plants are able to survive in matter.
(b) A burning candle stops burning if covered with a glass tumbler.
(c) Mountaineers and divers carry oxygen cylinders with them.
(d) When water is heated, we see bubbles rising up.
Answer:
(a) Fish and other water creatures need dissolved oxygen to respire and survive.
(b) When a candle burns in a closed jar, it uses up the available oxygen, causing the flame to die out.
(c) Low atmospheric pressure at high elevations means less oxygen for mountaineers, and divers underwater have no direct access to air, so both require supplemental oxygen.
(d) Heating water causes dissolved air to escape as bubbles; some of the water also evaporates into water vapor, which also appears as bubbles.
Question 6.
Name the processes which maintain the balance between oxygen and carbon dioxide in the air. How is it done?
Answer:
Photosynthesis and respiration are two fundamental biological processes that play crucial roles in maintaining the balance of gases in our atmosphere. Green plants perform photosynthesis, using sunlight, water, and carbon dioxide to create glucose for energy and releasing oxygen as a byproduct. Conversely, all living organisms, including plants themselves, undergo respiration, consuming oxygen and releasing carbon dioxide to produce energy. Essentially, photosynthesis removes carbon dioxide and adds oxygen, while respiration does the opposite, creating a vital cycle for life on Earth.
Question 7.
State two similarities and two differences between respiration and burning.
Answer:here are two similarities and two differences between respiration and burning:
Similarities:
- Both processes involve the breakdown of complex organic substances.
- Both release energy, often in the form of heat.
Differences:
- Respiration is a biological process that occurs in living organisms and is controlled by enzymes, while burning is a rapid chemical process that doesn’t require living cells or enzymes.
Question 8.
Define rusting ? What are the two necessary conditions for rusting of iron. Give the chemical name of rust.
Answer:That reddish-brown flaky stuff is indeed rust, chemically known as hydrated iron(III) oxide.
Question 9.
How is air useful to :
(a) water boats
(b) agriculture
(c) windmills
(d) scooters and cars.
Answer:(a) Water boats: You nailed it with sailboats! Wind, the movement of air, acts as a natural, clean force, pushing against the sails to glide the boat across the water.
(b) Agriculture: Plants are deeply connected to the air. They breathe in carbon dioxide for their food-making process (photosynthesis) and need oxygen for their roots to respire. Wind also plays a role in carrying pollen for fertilization. Of course, strong winds can sometimes be a bit too much, causing problems like soil erosion.
(c) Windmills: Exactly! Windmills are all about capturing the energy of moving air (wind). They transform this kinetic energy into mechanical power, which we can then use for things like grinding grains or even making electricity.
(d) Scooters and cars: Even though engines are the main power source, they rely on air for combustion. Plus, those air-filled tires give us a comfy and safe ride by providing cushioning and grip. On the flip side, cars and scooters have to work against air resistance as they move.
Question 11.
(a) Why is nitrogen important to all living beings ?
(b) What is nitrogen fixation ?
Answer:a) Absolutely! Nitrogen is indeed fundamental to life. It forms the very building blocks of proteins, which carry out countless tasks in our bodies, and DNA, the blueprint of life itself. No nitrogen, no life – it’s that crucial.
(b) You’ve got it. Nitrogen fixation is nature’s way of taking inert atmospheric nitrogen and transforming it into usable forms for plants. Special soil bacteria are the unsung heroes here, essentially unlocking this vital nutrient and making it available to all living things through the food web.
EXERCISE-III
Question 1.
What is air pollution ?
Answer:Air pollution happens when the air we breathe gets mixed with harmful stuff. This can be gases, tiny solid bits, or even liquids. Things like smoke from factories and cars, dust, and certain chemicals can make the air unhealthy for us and the environment.
Question 2.
Mention five causes of air pollution.
Answer:
Burning fossil fuels (vehicles, power plants).
Industrial emissions (factories).
Agricultural activities (pesticides, livestock).
Waste incineration (burning garbage).
Natural sources (volcanoes, dust storms).
Question 3.
Name two air pollutants which
(a) affect our health
(b) cause acid rain
(c) cause global warming.
Answer:
(a) Affect our health:
- Particulate Matter (PM)
- Carbon Monoxide (CO)
(b) Cause acid rain:
- Sulfur Dioxide (SO₂)
- Nitrogen Oxides (NOx)
(c) Cause global warming:
- Carbon Dioxide (CO₂)
- Methane (CH₄)
Question 4.
What is meant by ozone depletion?
Answer:Ozone depletion is basically the thinning of this important shield high up in the atmosphere that protects us from the Sun’s nasty UV rays. When it gets thin, more of that harmful radiation gets through, which isn’t good for any living thing. And the main culprits? Chemicals we humans created, like CFCs.
Question 5.
State four steps to be taken to control air pollution.
- Answer:Boost Public Transport & Go Green: Opt for buses, trains, or cycling and walking more often. Using electric vehicles also makes a big difference.
- Conserve Energy at Home: Simple things like switching off lights and fans when you leave a room and using energy-efficient appliances can really add up.
- Manage Waste Wisely: Reduce, reuse, and recycle to minimize the amount of waste that’s burned, which releases harmful pollutants.
- Support Cleaner Industries & Policies: Encourage businesses to adopt cleaner technologies and advocate for stronger environmental regulations.
Question 6.
Name three greenhouse gases.
Answer:
Carbon Dioxide
(CO₂)Methane (CH₄)
Nitrous Oxide (N₂O)
OBJECTIVE TYPE QUESTIONS
1. Fill in the blanks
OBJECTIVE TYPE QUESTIONS
- Fill in the blanks
(a) The layer of air around the earth is called the —–
Ans : Atmosphere.
(b) Although we cannot see air, we can—- it.
Ans : Feel
(c) Air is a—- of gases.
Ans : Mixture
(d) Plants and animals maintain the balance of carbon- —– in air.
Ans : Dioxide and oxygen
(e) Polluted air is—– for health.
Ans : Harmful
(f) The supporter of combustion in air is—–.
Ans : Oxygen
(g) Green plants need —— to prepare food.
Ans : CO2 water and light
(h) Oxygen is used in—- the food to get——.
Ans : Burning , Energy
(i) Aquatic plants and animals use —— in water.
Ans : Dissolved oxygen
(j) The reddish brown powder on the surface of iron nails exposed to air and moisture is called—.
Ans : Rust
2. Write ‘true’ or ‘false for the following
(a) Air is a compound.
Answer. False
Correct: Air is a mixture.
(b) Carbon dioxide is given out during photosynthesis.
Answer. False
Correct : Oxygen is given out during photosynthesis.
(c) Respiration needs nitrogen.
Answer. False
Correct: Respiration needs oxygen.
(d) The composition of air was discovered by Lavoisier.
Answer. True
(e) The major component of air is oxygen.
Answer. False
Correct: The major component of air is nitrogen
MULTIPLE CHOICE QUESTIONS
Tick (√) the correct alternative from the choice given for the following statements
1. Air consists of
- only oxygen
- only nitrogen
- only carbon dioxide
- all of these
Answer : All of these
2. Air pollution is due to the
- cutting of green plants
- gases like carbon monoxide, sulphur dioxide etc.
- smoke given out by factories
- all of the above
Answer: All of the above
3. The gases which cause acid rain are
- sulphur dioxide and oxygen
- nitrogen and oxygen
- carbon dioxide and water vapour
- nitrogen dioxide and sulphur dioxide
Answer : Nitrogen dioxide and sulphur dioxide
4. Rust is
- hydrated iron oxide
- hydrated copper sulphate
- anhydrous iron oxide
- none of the above
Answer: Hydrated iron oxide
5. Photosynthesis is a process in which plants
- take in oxygen and give out carbon dioxide
- take in carbon dioxide and give out oxygen
- take in nitrogen and give out oxygen .
- none of the above.
Answer : Take in carbon dioxide and give out oxygen
6. Fuels which do not leave any residue on burning are
- coal and wood
- coal and LPG
- wood and CNG
- LPG and CNG
Answer : LPG and CNG
7. Respiration
- is a slow process
- is a natural and continuous process
- takes place at body temperature
- all of the above
Answer : All of the above
8. Which of the following is common in combustion and respiration
- oxygen
- release of heat and light
- natural process
- nitrogen
Answer : Oxygen
9. Which of the following is not a greenhouse gas ?
- carbon dioxide
- sulphur dioxide
- methane
- Nitrogen
Answer : Nitrogen
10. The substance which accelerates the speed of a reaction without itself undergoing any change is called
- catalyst
- pollutant
- fuel
- none of the above
Answer : Catalyst
