Oxygen is returned to the atmosphere mainly by:

All living organisms are basically made up of $C, N, S, P, H$ and $O$. How do they enter the living forms? Discuss.

In what forms is water found on the Earth's surface? Describe in brief.

With the help of a labelled diagram,show the carbon cycle in nature. Describe the two ways in which carbon dioxide is fixed in the environment.

Write the names of two biologically important compounds that contain both nitrogen and oxygen.

Write the various components of soil.