Fill in the blanks.

1. _______________ per cent of the atmosphere is made of nitrogen.
2. Along with carbon dioxide and methane, _________ ___________ is a potent greenhouse gas.
3. The rate at which the temperature drops in the ___________ is 1ºC per 165 metres.
4. The __________ is the layer of the atmosphere that helps in radio transmission.
5. The upper part of the thermosphere is called the _____________.

Match the following.

Choose the correct answer.

1. This percent of the atmosphere is composed of nitrogen.
   1. 99
   2. 78
   3. 21
   4. 76
2. 21 per cent of the atmosphere is composed of
   1. helium
   2. oxygen
   3. nitrogen
   4. hydrogen
3. This gas protects us from the harmful ultraviolet radiation.
   1. oxygen
   2. ozone
   3. helium
   4. hydrogen
4. The rate at which the temperature drops in the troposphere is called
   1. lapse rate
   2. loss rate
   3. less rate
   4. drop rate
5. This layer of the atmosphere has the lowest temperature.
   1. mesosphere
   2. thermosphere
   3. tropopause
   4. stratosphere

State whether the following are true or false.

1. The earth's atmosphere contains 99 per cent oxygen, which is essential for life.
2. The stratosphere is the lowest layer of the atmosphere.
3. The temperature drops at the rate of 1ºC per 185 metres in the troposphere.
4. The stratosphere extends from the top of the troposphere up to 80 km above the earth.
5. Communication satellites orbit in thermosphere.

How is the atmosphere kept in place around the earth?