Explanation:

- Option 1: Jai Prakash Narayan was a prominent Indian independence activist and political leader. However, he did not head the Second Backward Classes Commission.

- Option 2: BP Mandal led the Second Backward Classes Commission, which was established in 1979. It is often referred to as the Mandal Commission.

- Option 3: VK Sahni is not associated with heading the Second Backward Classes Commission.

- Option 4: BR Ambedkar was a key figure in drafting the Indian Constitution but had no involvement with this commission, as it was established after his time.