Which of the following is a symbiotic microorganism?

Quite often,pulse crops are not manured with nitrogenous fertilizers. This is because:

What type of bacteria is $Rhizobium$?

Assertion : Nitrogen-fixing enzyme in legume root nodules functions at low oxygen concentration.
Reason : Low oxygen concentration is provided by leghaemoglobin.

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.

Knot-like bodies known as 'nodules' found in the roots of groundnut plant are produced by