“Neither... nor” is the correct correlative conjunction.
The verb agrees with the subject closest to it, which is “his wife” (singular), so we use “is” instead of “are.”
Thus, the correct answer is Option C.
Arun’s present age in years is 40% of Barun’s. In another few years, Arun’s age will be half of Barun’s. By what percentage will Barun’s age increase during this period?