Choose the correct sequence of True $(T)$ and False $(F)$ statements:
$(1)$ Zooplanktons are primary producers in an aquatic ecosystem.
$(2)$ Decomposition is largely an oxygen-requiring process.
$(3)$ In a natural ecosystem, fishes, wolf, etc., are carnivores.
$(4)$ The amount of energy decreases at each successive trophic level.

In a grassland ecosystem, match the trophic levels with their correct example species:

$(a)$ Fourth trophic level	$(i)$ Crow
$(b)$ Second trophic level	$(ii)$ Vulture
$(c)$ First trophic level	$(iii)$ Rabbit
$(d)$ Third trophic level	$(iv)$ Grass

Select the correct option:

Read the given statements and determine how many of them are correct.
$(1)$ Secondary succession depends on the condition of the soil and the availability of water.
$(2)$ Air,water,and land are abiotic factors of an ecosystem.
$(3)$ The structure of an ecosystem includes the cycling of nutrients and the unidirectional flow of energy.
$(4)$ The primary source of energy in an ecosystem is the sun.

Select the correct option from the following.

Identify the possible link '$M$' in the following food chain.
Plant $\rightarrow$ Insect $\rightarrow$ $M$ $\rightarrow$ Snake $\rightarrow$ Eagle

The world's most problematic aquatic weed is