Correct Answer - Option (B)
It's like semicircle of radius 1 unit is cut from the semicircle of radius 2 units and joined upside down to the semicircle of 2 units. So, the shaded area will be area of the semicircle with 2 units.
Hence, Shaded Area $ = \frac{1}{2}\cdot\pi \cdot (2^2) = 2 \pi$