Q1. Choose the correct option.
a.Shraddha lit a candle and covered it with a beaker. The candle extinguished after some time. Which gas present in the beaker was used during this process?
i.Oxygen
ii. Carbon dioxide iii. Nitrogen
iv. Hydrogen
Answer: i. Oxygen
b. The correct ascending order of gases as per their composition in the air is. i. nitrogen < hydrogen < oxygen
iii. carbon dioxide < oxygen < nitrogen
ii. hydrogen < carbon dioxide < nitrogen
iv. oxygen < carbon dioxide < hydrogen
Answer:iii. Carbon dioxide < Oxygen < Nitrogen
c.Mountaineers carry oxygen cylinders because as they climb:
- the layer of air becomes thin ii. The layer of air remains same iii. the layer of air becomes thick
iv. the amount of nitrogen increases the air
Answer:i. The layer of air becomes thin
d. Which activity will help to reduce air pollution?
I. Excess use of automobiles
ii. Reducing the use of recyclable material
iii. Increasing the use of alternative energy source
iv. Increasing the cutting of trees.
Answer: iii. Increasing the use of alternative energy sources
Q2. Assertion-Reasoning questions
Reducing the use of recyclable m Increasing the cutting of trees
For Questions number (i) and (ii), two statements are given – one labelled as A (A) and the other labelled as Reason (R). Select the correct answer to these c from (a), (b), (c) and (d) as given below.
(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct expla the Assertion (A).
(b) Both Assertion (A) and Reason (R) are true, and Reason (R) is not the correct e of the Assertion (A).
(c) Assertion (A) is true, but Reason (R) is false.
(d) Assertion (A) is false, but Reason (R) is true.
(i) Assertion (A): Oxygen is involved in respiration.
Reason (R): Plants and animals utilise carbon dioxide for respiration.
Answer: (c) Assertion (A) is true, but Reason (R) is false.
Explanation: Oxygen is used by plants and animals for respiration, not carbon dioxide. Plants use carbon dioxide for photosynthesis.
(i) Assertion (A): Breathing through the mouth allows germs to enter our body Reason (R): Fine hair and mucus present inside the nose prevent the dust from entering our body.
Answer: (a) Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
Explanation: The nose filters out dust and germs, which helps protect us. Mouth breathing can bypass this natural filter.
Q3.Name the following.
a. The component of air used in a fire extinguisher.
Answer: Carbon dioxide
b. The gaseous form of water.
Answer: Water vapor.
c. The component of air used to break down carbohydrates to release energy
Answer: Oxygen
d. The component of air that the plants cannot directly use, but is necessary for their growth.
Answer: Nitrogen.
Q4. Answer the following questions in one sentence.
a. What are pollutants?
Answer: Pollutants are harmful substances that make the air, water, or land dirty and unsafe.
b. What is humidity?
Answer: Humidity is the amount of water vapor present in the air.
c. Why do factories have tall chimneys?
Answer: Factories have tall chimneys to release smoke and pollutants high into the air to reduce pollution near the ground.
Q5. Give reasons for the following
a. Burning leads to an increase in atmospheric temperature.
Answer: Burning releases heat and gases like carbon dioxide, which trap heat in the atmosphere, causing temperatures to rise.
b. Vehicles that run on solar energy are more environmental friendly than those that run on petrol.
Answer: Solar-powered vehicles do not release harmful gases, unlike petrol vehicles, which pollute the air.
c.In a bucket filled with water, if you dip an empty bottle straight upside down to the bottom of the bucket, the water will not enter the bottle.
Answer: Air trapped inside the bottle prevents water from entering, as there is no space for the water to fill.
Q6 . Answer the following questions.
a. How is the net oxygen present in the atmosphere sufficient to support and sustain all forms of life?
Answer: The amount of oxygen in the atmosphere stays balanced because of the oxygen cycle. Plants produce oxygen during photosynthesis, which animals and humans use for breathing. This balance ensures that oxygen is always available.
b. List down any three steps that can be taken to reduce air pollution.
Answer:
- Use public transportation or carpool to reduce the number of vehicles on the road.
- Use alternative energy sources, like solar or wind, instead of burning fossil fuels.
- Plant more trees, as they absorb carbon dioxide and release oxygen.
- How is air Useful to us ? (Give any five points)
Answer:
- Breathing: We need oxygen from the air to breathe and live.
- Photosynthesis: Plants use carbon dioxide from the air to make food and release oxygen.
- Burning Fuel: Oxygen in the air is needed to burn fuels for cooking, heating, and transport.
- Pollination: Air helps spread pollen, which allows plants to reproduce.
- Weather: Air plays a big role in forming clouds, rain, and weather patterns that support life.