(a) "The number of questions that you ask is never ending."
This sentence is correct with minor formatting adjustments.
(b) "All the food that you have ordered for your friends is going waste."
This sentence is correct with minor correction.
(c) "Most of the birds will be migrating to safer places within winter."
This sentence is incorrect due to the incorrect preposition.
(d) "I find it difficult to paying attention to his constant complaints."
This sentence is incorrect due to incorrect verb usage.
Sentences (a) and (b) are correctly structured. Therefore, the correct answer is (A) a and b.
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?