Nitrogen-fixing bacteria make combination with cells of the roots of

The answer is A) Pulses. The bacterium is Rhizobium, which forms root nodules with leguminous plants such as gram, moong, arhar, lentil and peas. Inside these nodules, the bacteria convert atmospheric N₂ into ammonia using the enzyme nitrogenase. The plant gets usable nitrogen, and the bacteria get carbohydrates and shelter. Leghaemoglobin in the nodule keeps oxygen away from nitrogenase. This is a symbiotic association.

• Rice: Not a legume. Its nitrogen gains come from free-living or associative fixers such as Azospirillum, and from the Anabaena partner in Azolla, with no nodules.
• Wheat: Non-leguminous. Associative bacteria like Azotobacter colonise the rhizosphere without forming nodules.
• Sugarcane: Gluconacetobacter diazotrophicus lives inside the plant as an endophyte. It does not form nodules, so it does not fit the question's wording.

This sits in Agriculture and Environment, and it links to Mains questions on crop rotation, biofertilisers and reducing fertiliser subsidy dependence.

Trap: Students pick sugarcane or rice because they have read about endophytic or Azolla-based fixation. The key word is nodules, and only legumes form them.