"If you had told me the truth, I would have helped you" is correct because it follows the proper structure for a third conditional sentence, which is used for hypothetical situations in the past.
The other sentences are grammatically incorrect:
The sentence "If you had told me the truth, I would have helped you" is correct, while the other sentences contain grammatical errors or awkward phrasing.
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?