Answer:
b) earths atmosphere contains 21% oxygen.
Explanation:
The atmosphere is the envelope of air surrounding the Earth. The air composed of gases. In the atmosphere, the percentage of different gases differ. Nitrogen comprises 78.08 %, oxygen is 20.95%, and carbon dioxide is another important gas which consists of 0.036%. In the atmosphere, water vapour is 0 to 4%.
It is divided up into layers or spheres such as troposphere, stratosphere, mesosphere. The troposphere is lowermost layers in which living organisms found. In the stratosphere, the ozone layer is present which absorbs harmful ultraviolet radiation (UV rays) which are coming from the sun. So, it protects life from its harmful effect.
