Step 1: Understanding the Concept:
The National Board for Wildlife (NBWL) is a statutory organization constituted under the Wildlife (Protection) Act, 1972.
It serves as an apex advisory body on all policies and measures related to forest conservation and wildlife protection in India.
Step 2: Detailed Explanation:
The National Board for Wildlife (NBWL) is highly influential, as its approval is required for all projects inside or within a $10\text{ km}$ radius of national parks and wildlife sanctuaries.
Due to its strategic importance, the board is headed by the head of the national executive:
- The Prime Minister of India serves as the ex-officio Chairman of the NBWL.
- The Union Minister of Environment, Forest and Climate Change serves as the ex-officio Vice-Chairman of the board.
The board includes $47$ members, which include members of parliament, conservationists, ecologists, and government officials from various ministries.
The other options are incorrect because:
- The Union Minister of Environment, Forest and Climate Change is the Vice-Chairman, not the Chairman.
- The Secretary of the Ministry of Environment and Chief Secretaries of states serve as members or facilitators, not the head of the board.
Step 3: Final Answer:
The Prime Minister of India is the ex-officio Chairman of the National Board of Wildlife.