In which of the following angiosperms do the root nodules contain filamentous nitrogen-fixing microorganisms?

Rhizobium lives symbiotically with root nodules and fixes atmospheric nitrogen. It provides nitrogenous compounds to the host and in turn takes food from the host. This food taken by the bacterium is:

Leghaemoglobin helps in

Which pigment is essential for $N_2$ fixation in plants of the family Leguminosae?

The free-living nitrogen-fixing cyanobacterium that forms a symbiotic association with the aquatic fern Azolla is ............. .

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 $Alnus$. What kind of relationship is observed between mycorrhiza and pine trees?