A prokaryotic autotrophic nitrogen-fixing symbiont found in?

The correct option is C

Cycas

The correct option is C.

Explanation of correct option:

1. Cycas is a gymnosperm that belongs to the family Cycadaceae.
2. They contain a special type of root called coralloid roots.
3. Anabaena cycadeae is a prokaryotic, blue-green algae. They are autotrophs and are mostly found in the coralloid roots.
4. Anabaena forms a symbiotic relationship with Cycas plants and helps in nitrogen fixation.

Explanation of incorrect option:

Option A:

1. In Cicer plants, nitrogen fixation is carried out by Rhizobium.
2. Rhizobium is a free-living, heterotrophic bacteria found in the soil.

Option B:

1. In Pisum plants, Rhizobium forms a symbiotic relationship with roots.
2. Rhizobium, a heterotroph, helps in nitrogen fixation.

Option D:

1. Nitrogen fixation is also observed in non-leguminous plants such as Alnus.
2. In Alnus, nitrogen fixation is carried out by Frankia (a heterotroph).

Final answer: A prokaryotic autotrophic nitrogen-fixing symbiont found in Cycas.