Which of the following protects nitrogenase inside the root nodule of a leguminous plant?

$A$: Bacteria enter only the polyploid cells of the root cortex.
$R$: These cells provide cytokinins to bacteria,which promote bacterial cell division.

Arrange the stages of root nodule formation in the correct sequence:
$I-$ Infection thread is produced.
$II-$ Bacteria are carried to the cortex of the root.
$III-$ Bacteria attach to the root hair.
$IV-$ Bacteria are released from the thread into the cells.
$V-$ Differentiation into nitrogen-fixing cells occurs.

If a wheat field is inoculated with $Rhizobium$,what will be the effect on the soil?

We find that $Rhizobium$ forms nodules on the roots of leguminous plants. Also,$Frankia$,another microbe,forms nitrogen-fixing nodules on the roots of the non-leguminous plant $Alnus$. Is it necessary for a microbe to be in close association with a plant to provide mineral nutrition? Explain with the help of one example.

Root nodules for nitrogen fixation of a non-leguminous tree possess