The correct answer is option 4, Prime Minister. The Chairman of NITI Aayog, which stands for National Institution for Transforming India, is the Prime Minister of India. NITI Aayog is a policy think tank of the Indian government that aims to provide strategic and policy inputs to promote sustainable and balanced development across various sectors. As the Chairman of NITI Aayog, the Prime Minister plays a crucial role in guiding and shaping the policies and initiatives of the organization. While the President, RBI Governor, and Finance Secretary hold significant positions in the Indian government, they do not serve as the Chairman of NITI Aayog.