Radius of the Mohr’s circle, charactering the state of stress at the point, is

Question

A two dimensional fluid element rotates like  rigid body. At  point with in the element, the pressure is 1 unit. Radius of the Mohr’s circle, charactering the state of stress at the point, is                                         

      (a) 0.5 unit                                                          (b) 0 unit

      (c) 1 unit                                                             (d) 2 units