The correct answer is Sarpanch.
A Sarpanch is the elected head of a Gram Panchayat, the smallest unit of self-government in India. The Sarpanch is elected by the members of the Gram Panchayat, who are in turn elected by the voters of the village. The Sarpanch is responsible for the day-to-day running of the Gram Panchayat and for implementing the decisions of the Gram Sabha, the village assembly.
The Pradhan is the head of a Panchayat Samiti, a local government body in India that is responsible for a group of villages. The Pradhan is elected by the members of the Panchayat Samiti, who are in turn elected by the voters of the villages in the Panchayat Samiti. The Pradhan is responsible for the day-to-day running of the Panchayat Samiti and for implementing the decisions of the Panchayat Samiti Sabha, the assembly of the Panchayat Samiti.
The Panchayat Secretary is a government employee who is responsible for the administration of a Gram Panchayat. The Panchayat Secretary is appointed by the State Government and is responsible for carrying out the orders of the Sarpanch and the Gram Panchayat.
The Block Development Officer is a government employee who is responsible for the administration of a Block, a unit of administration in India that is larger than a Panchayat Samiti but smaller than a district. The Block Development Officer is appointed by the State Government and is responsible for carrying out the orders of the District Magistrate and the Block Development Committee.