The correct answer is: 660 sq km.
As per India State of Forest Report, 2017, the reserved forest area of Bihar is 660 sq km. This is about 1.4% of the total geographical area of the state. The reserved forests are managed by the Forest Department of the state government. They are important for the conservation of biodiversity and for the provision of ecosystem services such as water regulation, soil conservation, and climate regulation.
The other options are incorrect. Option A is incorrect because it is the area of the protected forest in Bihar. Option B is incorrect because it is the area of the unclassed forest in Bihar. Option C is incorrect because it is the area of the non-forest area in Bihar.