Which of the following statements is correct regarding secondary succession?

Read the following statements carefully and answer the question given below:
$(1)$ $NPP = GPP - R$
$(2)$ Productivity of an ecosystem can be measured in $g/m^2/yr$ or $kcal/m^2/day$.
$(3)$ The total amount of energy produced by all producers in an ecosystem is called Gross Primary Productivity $(GPP)$.
$(4)$ The net primary productivity of the oceans is $55$ billion tons.
State the number of correct statements.

Match the columns:

Column-$I$	Column-$II$
$(a)$ Decomposers	$(i)$ Bacteria
$(b)$ Primary productivity	$(ii)$ Consumers
$(c)$ Natural ecosystem	$(iii)$ Producers
$(d)$ Secondary productivity	$(iv)$ Forest

Succession proceeds from

The first link in any food chain is a green plant because

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