Crystalline rocks are a natural source of which biogenetic element?

Which among the following is not a functional unit of the ecosystem?

If less light falls on the pond's surface,what is the most likely consequence for the fish population?

Select the incorrect statement for the detritus food chain.

Consider the following statements about food chain:
$I.$ The transfer of energy from producers to top consumers through a series of organisms is called a food chain.
$II.$ $A$ food chain is always straight and proceeds in a progressive straight line.
$III.$ In a food chain,there is a unidirectional flow of energy from the sun to producers and subsequently to a series of different types of consumers.
Which of the statements given above are correct?

Maximum absorption of rainfall water is done by