Define denitrification.

Assertion $\left(\mathrm{A}\right):$ Free-living bacteria such as Rhizobium and Frankia can help in the biological fixation of dinitrogen in the roots of angiospermous plants.

Reason $\left(\mathrm{R}\right):$ Prokaryotes exclusively contain nitrogenase enzyme which can catalyze the oxidation reaction of dinitrogen to glutamate.

The correct answer is:

Rhizobium forms a symbiotic association with roots in legumes and fixes atmospheric nitrogen. Which of the following statement is correct about this process?

Study the following illustration of nitrogen cycle and identify $\mathrm{A}, \mathrm{B}$ and $\mathrm{C}$ in it.

Assertion (A):- Some plants growing in ${\mathrm{N}}_2$ rich soils can obtain their nitrogen from insects.

Reason R): - Bacteria inhabiting the root system of Fabaceae plants can fix atmosphere nitrogen.

The correct option among the following is:

Match Column - I with Column - II.

Microbes are useful to human beings in diverse ways. If so, name the following:

Symbiotic nitrogen-fixing bacterium.

The nitrogen cycle is given below. Identify A and B in it.