We need to solve this problem Conceptually, rather mathematically. Suppose a situation, where this body comprises of only a single particle at a distance R, so centre of mass should be at R only. Now, if this body has a regular distribution of particles at a distance R from origin (i.e. circular in case of 2D or spherical in case of 3D) then the centre of mass should be somewhere between origin and R. so, combining these two cases we can tell, CoM ≤ R.