In the figure shown alongside, side length of the square is 2a units.

Assertion (A): Area of smaller circle = Area enclosed between two circles.
Reason (R):Radius of outer circle (Radius of inner circle).
(1)
Let R and r be the radii of outer and inner circle respectively.
Diameter of inner circle = 2a

Both Assertion (A) and Reason (R) are true and Reason (R) is correct explanation of Assertion (A).