Nitrogen availability is often a limiting factor in plant growth. nitrogen tends to be scarce because
a) fossil fuel combustion uses the available nitrogen; what is left for the plants is not enough, making the fuel combustion a limiting factor.
b) decomposers are unable to recycle nitrogen, meaning that all nitrogen used must be produced by bacteria.
c) there is very little nitrogen present in the atmosphere.
d) nitrogen gas (n2) is so stable that only a few organisms are capable of turning it into nitrogen that can be used for living things.

D) Nitrogen gas (N2) is so stable that only a few organisms are capable of turning it into nitrogen that can be used for living things.

Explanation:

Nitrogen cycle is very important for the growth and development of the plants. This is because of the fact that nitrogen being in the form of nitrogen gas in the atmosphere cannot be absorbed by the plants readily instead it should be converted into forms which can be utilized by the plants. Only few organisms particularly some strains of bacteria can perform the task of nitrogen fixation in the soil.    

from the original order (top to bottom) the new order will go

1 (founder)

4 (hawk)

2 (mutate)

3 (next generation)

haploid cells;