The correct answer is C. 6,183 sq km.
The protected forest area of Bihar is 6,183 sq km. This is about 6.5% of the total geographical area of the state. The protected forests are managed by the Forest Department of the Government of Bihar. The main objective of the protected forests is to conserve the biodiversity of the state. The protected forests also provide a number of other benefits, such as watershed protection, soil conservation, and carbon sequestration.
Option A is incorrect because it is the area of the protected forests in the state of Jharkhand. Option B is incorrect because it is the area of the protected forests in the state of Uttar Pradesh. Option D is incorrect because it is the area of the protected forests in the state of Madhya Pradesh.