Question

A crop plant which can grow well even in nitrogen-deficient soil is
A) Helianthus campestris
B) Gossypium herbaceum
C) Brassica campestris
D) Cajanus cajan

Answer 1

Hint: Generally the plants to grow properly contain some essential things such as sunlight and water, apart from this soil where the plant grows should have all essential nutrients, but some plants such as plants that belong to Fabaceae or legume plants can grow even in nitrogen-deficient soil.

Complete step-by-step answer:
Legume plants have bacteria in their roots called rhizobium which is able to fix the atmospheric nitrogen into the soil, so because of this these plants even can grow in Nitrogen deficient soil.
 On the earth, among all gases, 80% of Earth's atmosphere is made up of nitrogen gas (N), but Unfortunately, this Nitrogen is mostly not used by many of the living organisms.
Most of the plants we and other animals, and microorganisms we can see are dying of nitrogen deficiency even though they have enough available nitrogen, but this cannot be used.
Most of the organisms use the ammonia ($NH_3$) form of nitrogen for the production of various biological substances such as amino acids, from which proteins and nucleic acids, and some other nitrogen-containing components which are generally essential or necessary for life.
The process of Biological nitrogen fixation is the conversion of the inert N that present in the atmosphere to a biologically useful form of nitrogen such as $NH_3$
Some plants such as ones that belong to Fabaceae where we commonly called legume plants to get benefit from N-fixing bacteria which are present in their roots, and when these bacteria die they release nitrogen to the environment.
Most of the legume plants and some other plants possess bacteria that live in roots as small nodules where bacteria live Within these nodules, nitrogen fixation is done by the bacteria, and the NH3 they produce is absorbed by the plants. Here the plants and the bacteria are in symbiotic relation, with each other.
Among all above given options Cajanus cajan is a plant belonging to Fabaceae which possess rhizobium bacteria in their roots, so it is the correct option.

Option D is the correct answer.

Note: Biological nitrogen fixation can be seen in other forms of life such as blue green algae, and some free soil bacteria, lichens which fix some of the atmospheric nitrogen into $NH_3$ but these biological forms cannot be utilized by crop plants.