Total earth's surface covered by water is: (in $\%$)

Name two factors that make soil fertile.

The process of nitrogen-fixation by bacteria does not take place in the presence of

There is mass mortality of fishes in a pond. What may be the reasons?

"Soil is formed by water." If you agree with this statement, provide reasons.

State whether the following statement is True or False:
Oxygen is necessary for life for most organisms in the process of respiration,but some forms of life,especially bacteria,are poisoned by elemental oxygen.