Which of the following statements is true for an ecosystem?

The maximum evolution of oxygen is by which of the following producers of organic matter?

What is true about the phosphorus cycle?
$I.$ Rocks are the natural reservoirs of phosphorus.
$II.$ Weathering of sedimentary rocks makes phosphate available to the soil.
$III.$ Herbivores and carnivores obtain phosphorus from plants directly or indirectly.
Choose the correct option.

$A$: In hydrosere,the reed swamp stage is followed by the floating plant stage.
$R$: The sedge meadow stage has amphibious herbaceous plants.

Given below are four statements $(a-d)$ each with one or two blanks. Select the option which correctly fills the blanks in two statements.
$(a)$ Ecological succession is a ...$(i)$... and fairly predictable change in the ...$(ii)$... of a given area.
$(b)$ In ecological succession,the entire sequence of communities that successively change in a given area is called ...$(i)$....
$(c)$ Primary succession occurs on ...$(i)$....
$(d)$ Secondary succession is ...$(i)$... than primary succession.

Maximum biomass and variable organisms are found in