The correct answer is option 4, the Cabinet Secretary. The Chairman of the Steering Committee to oversee the functions of the National Authority, Chemical Weapons Convention (CWC) is the Cabinet Secretary.

Let`s analyze the other options to understand why they are not the correct answer.

Option 1, the President, is incorrect because the President`s role is mainly focused on the executive power of the state and not specifically involved in overseeing the functions of the National Authority, CWC.

Option 2, the Prime Minister, is also incorrect. While the Prime Minister holds a significant role in the government, overseeing the functions of the National Authority, CWC is not within their direct responsibilities.

Option 3, the National Security Adviser, is also not the correct answer. The National Security Adviser`s primary responsibility is to advise the government on matters of national security and coordinate national security policies. Although the Chemical Weapons Convention may have implications for national security, overseeing its functions is not the role of the National Security Adviser.

Therefore, the correct answer is option 4, the Cabinet Secretary. The Cabinet Secretary is the head of the Indian Administrative Service and is responsible for coordinating and overseeing the functioning of the government.