Which crop has the capacity to fix most of CO₂ in the form of organic acid in drought condition?

Correct option is A

Soyabean (a C3 plant) under drought stress can shift its carbon fixation metabolism to accumulate organic acids like malate to some extent.
However, C4 and CAM plants have higher capacity for CO₂ fixation in the form of organic acids, but among the given options, soyabean shows relatively higher adaptability through osmotic adjustment and partial acid accumulation under drought.
Explanation:
(a) Soyabean – Has moderate drought tolerance and accumulates organic acids like malate under stress, making it relatively efficient in fixing CO₂ during drought.
(b) Gram – Though drought-tolerant, it does not fix CO₂ in the form of organic acids significantly.
(c) Moong – A pulse crop with some drought resistance, but not known for organic acid accumulation under drought.
(d) Urd – Also a pulse crop; like moong, it lacks significant CO₂ fixation via organic acids in drought.