India's patent term was harmonised with international norms when the Patents (Amendment) Act, 2005 came into force to meet obligations under the TRIPS agreement. From that point onward, Section 53 fixes a uniform term of twenty years from the filing date for every patent, whether it protects a product or a process, and irrespective of the technical field of the invention. None of the other durations, ten, thirty, or forty years, appear anywhere in the Act; they are simply not timelines recognised under Indian patent law.
Therefore, the correct answer is 20 Years.