Who among the following is the main officer in-charge of the district…

In Indian state administrative structure, a state is organised into nested units for general and revenue administration: division, district, sub-division, and tehsil. Each unit has its own designated head officer responsible for administration at that specific level.

The District Collector (also called District Magistrate in some states) is the officer appointed to head the overall general administration of a single district. This officer coordinates revenue work, exercises magisterial authority for law and order, and supervises development and welfare programmes running within that district.

• S.D.O. (Sub-Divisional Officer) heads a sub-division, a smaller unit comprising a group of tehsils within a district, not the district as a whole.

• Tehsildar heads a tehsil, the smallest revenue administrative unit, primarily handling land records and revenue collection at that local level.

• Divisional Commissioner heads a division, a larger unit made up of several districts, one administrative level above the district itself.

Since the district itself is the unit named in the question, and only the District Collector's charge matches the district as a whole, District Collector is the correct answer.