What is the $SI$ unit of the radius of gyration?

The moment of inertia of a sphere of mass $M$ and radius $R$ about an axis passing through its centre is $\frac{2}{5} M R^2$. The radius of gyration of the sphere about a parallel axis to the above and tangent to the sphere is

$A$ uniform solid cylinder of length $L$ and radius $R$ has a moment of inertia about its axis equal to $I_1$. $A$ small co-centric cylinder of length $L/2$ and radius $R/3$ is carved from this cylinder. The moment of inertia of this small carved cylinder about the same axis is $I_2$. The ratio $I_1/I_2$ is . . . . . . .

The radius of gyration of a disc of mass $50 \, g$ and radius $2.5 \, cm$ about an axis passing through its center of gravity and perpendicular to its plane is ....... $cm$.

The moment of inertia of a straight thin rod of mass $M$ and length $l$ about an axis perpendicular to its length and passing through its one end,is

Two discs having moment of inertia $I_1$ and $I_2$ are made from the same material and have the same mass. Their thicknesses and radii are $t_1, t_2$ and $R_1, R_2$ respectively. The relation between the moment of inertia of each disc about an axis passing through its centre and perpendicular to its plane and its thickness is: