The correct option is B curiosity
Option D: The word 'curiosity' refers to 'a strong desire to know or learn something'. It is relevant in meaning to the given sentence, as the words "always asking questions" defines a curious person. Hence option D is correct.
Option A: 'Ability' is the skill or talent to do something. It isn't relevant here, as a result the sentence sounds vague. Hence A is incorrect.
Option B: 'Felicity' is an intense happiness. It has no relation to the given sentence. Hence B is incorrect.
Option C: A calamity is an event that causes great damage, a disaster. It does not refer to the quality of a person (Rajesh). Hence C is incorrect.