A uniform disc of radius R rolls without slipping  on a rough horizontal surface.  At an instant, A is the lowest particle of the disc and C is the centre of disc. Then the location of particles on the disc at that instant, whose normal acceleration is zero, can be:

Take a point P on disc at a distance x from A, such that AP makes an angle  with vertical diameter of disc. Then the normal acceleration of P is  ${\omega }^{2}x-{\omega }^{2}R\cos \theta$ towards A.  Then the locus of points whose normal acceleration is zero are given by  $x=R\cos \theta$. This is a circle with diameter AC