The area of a square = 16 sq. units

Let x denote the side of the square.

Then, area of the square = x² = 16

                  (Take square root each side)

Length is always positive, so x = 4.

The diameter of the circle = side of the square = 4

Therefore the radius of the square =

Area of the circle =  sq. units

Square units.

Option C is right choice.