A clean dry sample of air is made up of …………… percent nitrogen:

1. 72
2. 77
3. 78
4. 79

About 90 percent of air mass lies within about …………… from the earth's surface.

1. 20 km
2. 22 km
3. 25 km
4. 30 km

Name the densest layer of the atmosphere.

1. Exosphere
2. Troposphere
3. Stratosphere
4. Mesosphere

Name the layers as we move from space to the surface of the earth.

1. Thermosphere - Mesosphere - Stratosphere - Troposphere
2. Troposphere - Mesosphere - Stratosphere - Thermosphere
3. Troposphere - Stratosphere - Mesosphere - Thermosphere
4. Thermosphere - Stratosphere - Mesosphere - Troposphere