Correct option is D
Given:
Arun walks 8 km in West direction.
Then he turns 90° anticlockwise.
Here,
Starting Direction: Arun walks in the West direction.
Turn: He turns 90° anticlockwise (counter-clockwise).
Final Direction: A 90° anticlockwise turn from West leads to South.

So, In South direction is he facing now
Hence, the correct answer is "Option D".