The correct answer is A. Seraikela-Kharsawan.
The ocean affected zone of Jharkhand falls in the region of Seraikela-Kharsawan. This is because the district is located on the banks of the Subarnarekha River, which is a tributary of the Ganges River. The Subarnarekha River is a major source of water for the district, and it is also a major transportation route. The district is also home to a number of industries, which rely on the river for water and transportation.
The other options are incorrect because they do not fall on the banks of the Subarnarekha River. Option B, Santhal Pargana, is a large district in Jharkhand that is located in the eastern part of the state. Option C, West part of Jharkhand, is a large region that includes a number of districts in the western part of the state. Option D, Palamu-Garhwa, is a small district in the northern part of the state.