$A$ legume having symbiotic association with two nitrogen-fixing bacteria ($Rhizobium$ and $Aerorhizobium$) is

$Frankia$ is free-living in soil,but as symbionts,can fix atmospheric nitrogen.

Select the correct statements from the given:
$(a)$ Nitrogenase is a heterodimeric protein.
$(b)$ Root hairs curl by action of nitrogenase and plant 'nod factors'.
$(c)$ During symbiotic $N_2$ fixation,$ATP$ is provided by the legume plant.

Red pigment $(Leghaemoglobin)$ having affinity for oxygen is present in the roots of

Which of the following is responsible for nitrogen fixation in an aquatic fern?

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