1. The atmosphere is a mixture of several gases. Near the earth’s surface contains mainly:
(a) Nitrogen and oxygen
(b) Nitrogen and carbon dioxide
(c) Oxygen and carbon dioxide
(d) Ethane and oxygen
[R.A.S./R.T.S. (Pre) 1997]
Ans. (a) Nitrogen and oxygen
- The composition of the atmosphere consists of a variety of gases, with Nitrogen (78.08%) and Oxygen (20.95%) being the predominant gases, making up approximately 99% of the total.
- The remaining 1% comprises gases such as Argon, Carbon dioxide, Neon, Helium, Methane, Hydrogen, Nitrous Oxide, Ozone, Krypton, Xenon, and others.
- Within the atmosphere, heavier gases tend to be concentrated closer to the Earth’s surface, while lighter gases are found higher up.
- Carbon dioxide, for instance, can be found up to 20 km above the Earth, while Oxygen and Nitrogen are present up to 100 km.
- Hydrogen, on the other hand, can be found up to 125 km.
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2. The correct sequence of different layers of the atmosphere from the surface of the Earth upwards is :
(a) Troposphere, Stratosphere, Ionosphere, Mesosphere
(b) Stratosphere, Troposphere, Ionosphere, Mesosphere
(c) Troposphere, Stratosphere, Mesosphere, Ionosphere
(d) Stratosphere, Troposphere, Mesosphere, Ionosphere
[I.A.S. (Pre) 1998]
Ans. (c) Troposphere, Stratosphere, Mesosphere, Ionosphere
- The atmosphere is divided into five layers from the Earth’s surface based on temperature and air pressure.
- These layers are:
- Troposphere – (15 km from the surface of the earth)
- Stratosphere – (15-50 km)
- Mesosphere – (50-80 km)
- Ionosphere – (80-640 km)
- Exosphere – (above more than 640 km)
- So option (c) is correct.
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3. Most weather activity occurs in which atmospheric layer:
(a) Ozonosphere
(b) Ionosphere
(c) Troposphere
(d) Exosphere
[R.A.S./R.T.S. (Pre) 1999]
Ans. (c) Troposphere
- Rain, fog, hail, and other types of weather happen in the troposphere.
- The temperature in this layer goes down by 6.5°C for every 1000 meters (1 km) of height.
- This layer is very important for life.
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4. The stratosphere is said to be ideal for flying jet aircraft. This is because-
(a) This layer is rich in ozone which reduces fuel consumption
(b) The temperature is constant and ideal for aircraft engine efficiency
(c) This layer is out of the firing range of anti aircraft guns
(d) The absence of clouds and other weather phenomena
[Jharkhand P.C.S. (Pre) 2010]
Ans. (d) The absence of clouds and other weather phenomena
- The stratosphere is the second layer of the atmosphere, located above the troposphere and below the mesosphere.
- This layer has very little water vapour, so there are no clouds or weather events.
- This makes it a great place for jets to fly since there won’t be any disturbances.
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5. The ozone layer lies in the :
(a) Troposphere
(b) Tropopause
(c) Stratosphere
(d) Photosphere
[Chhattisgarh P.C.S. (Pre) 2011, Uttarakhand P.C.S. (Pre) 2010, U.P.P.C.S. (Pre) 1997]
Ans. (c) Stratosphere
- The ozone layer is found in the lower part of the atmosphere between 15 and 20 kilometres above the Earth’s surface.
- It can reach up to 55 kilometres, but has its highest concentration between 15 and 20 kilometres.
- This layer absorbs ultraviolet radiation, protecting life on Earth from its harmful energy, which can cause skin cancer.
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6. Which one of the following layers of the atmosphere is responsible for the deflection of radio waves?
(a) Troposphere
(b) Stratosphere
(c) Mesosphere
(d) Ionosphere
[U.P.P.C.S. (Mains) 2005, I.A.S. (Pre) 1996]
Ans. (d) Ionosphere
- Radio signals (important for wireless communication) bounce off the Ionosphere.
- The ionosphere is the top layer of the atmosphere, located starting at around 80 km in the air and extending beyond 1000 km.
- It is made of ions, which are electrons that are released when sunlight hits the gas molecules in the air.
- It is an electrically conductive layer which helps radio waves travel and is used for telecommunication.
- This area also has cosmic rays and the Northern and Southern lights (Aurora Borealis and Aurora Australis).
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7. Which layer of the atmosphere is responsible for Aurora Borealis?
(a) Troposphere
(b) Thermosphere
(c) Ionosphere
(d) Exosphere
[U.P.P.C.S (Pre) 2010]
Ans. (c) Ionosphere
- Aurora is a beautiful display of lights that is caused by tiny particles from the Sun that hit the Earth’s atmosphere.
- In the Northern Hemisphere, it is called Aurora Borealis and in the Southern Hemisphere, it is called Aurora Australis.
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8. In which atmospheric layer are communication satellites located?
(a) Exosphere
(b) Stratosphere
(c) Ionosphere
(d) Troposphere
[Uttarakhand P.C.S. (Pre) 2005, R.A.S./R.T.S. (Pre) 1997]
Ans. (a) Exosphere
- Geostationary satellites are located very high up in the sky, around 36000 km above the Earth.
- The Exosphere is the outer layer of our atmosphere, which starts at a height of 640 km from the ground.
- So, these communication satellites are found in the Exosphere.
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9. Which of the following is correct in matching the layer of atmosphere and its characteristics?
1. Troposphere – Weather Phenomena
2. Stratosphere – Ozone layer
3. Ionosphere – Radio waves reflected to Earth’s surface
4. Mesosphere – Aurorae
Code :
(a) 1, 2, 3 and 4
(b) 1, 2 and 4
(c) 1, 2, and 3
(d) 2 and 3
[U.P.P.C.S. (Mains) 2002]
Ans. (c) 1, 2, and 3
- Weather such as rain, fog, and hail happens in the troposphere.
- The stratosphere has a layer of ozone gas.
- Radio signals sent from the ground bounce off the ionosphere and come back.
- Aurora lights occur in ionosphere only, so options 1, 2, and 3 are true but option 4 is wrong.
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