$A$ crop plant which can grow well even in nitrogen-deficient soil is:

Root nodules contain

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

Trace the events starting from the coming in contact of Rhizobium to a leguminous root till nodule formation. Add a note on the importance of leghemoglobin.

Give scientific reasons:
$(1)$ Leguminous plants are rich in protein.

Which of the following statements is correct regarding nitrogen fixation in legumes?