(b) 8 m.
Let AC = 2x, OB = 2y.
∴ Radius = OC = 2y = OB
From Δ ODC,
OC2 = OD2 + CD2
⇒ 4y2 = y2 + x2 ⇒ x2 = 3y2 ⇒ x = √3 y … (1)
Also,
Area of Δ ODC = \(\frac12\) × Area of rhombus OABC
⇒ \(\frac{1}{2}\times{x}\times{y}\) = \(\frac14\) x 32√3 ⇒ xy = 16√3 ......(2)
From (1) and (2) we have, y = 4 and x = 4√3
∴ Radius of the circle = 2y = 8 m.