The radius of gyration of a solid sphere of radius R about a certain axes is also equal to R. If r is the distance between the axes and the centre of a sphere , then r is equal to

Question

$\begin {array} {1 1} (1)\;R & \quad (2)\;0.5 R \\ (3)\;\sqrt { 0.6}R & \quad (4)\;Zero \end {array}$