Explanation:

- The 15th Finance Commission of India is tasked with defining the financial relations between the central government and the states for 2020-2025.

- Option 1: Ramesh Chand

- Ramesh Chand is an eminent agricultural economist and a member of NITI Aayog, but he is not the chairman of the 15th Finance Commission.

- Option 2: Subhash Chandra Garg

- Subhash Chandra Garg is a retired Indian Administrative Service officer, but he has no direct connection to the leadership of this Finance Commission.

- Option 3: NK Singh

- NK Singh was indeed appointed as the chairman of the 15th Finance Commission of India. His extensive experience in public service and finance led to this prominent appointment.

- Option 4: Arvind Mehta

- Arvind Mehta is a seasoned bureaucrat with expertise in trade, but he is not associated with the 15th Finance Commission as its chairman.