The theorem of perpendicular axes is applicable to which type of body?

Two identical spheres, each of mass $2 \,kg$ and radius $50 \,cm$, are fixed at the ends of a light rod so that the separation between their centers is $150 \,cm$. The moment of inertia of the system about an axis perpendicular to the rod and passing through its middle point is $\frac{x}{20} \,kg \,m^2$. Find the value of $x$.

For the given uniform square lamina $ABCD$,whose centre is $O$,

What is the moment of inertia of a disc about one of its diameters?

$A$ thin uniform rod has mass $M$ and length $L$. The moment of inertia about an axis perpendicular to it and passing through the point at a distance $\frac{L}{3}$ from one of its ends,will be

Three rods are arranged in the form of an equilateral triangle. Calculate the moment of inertia about an axis passing through the centroid and perpendicular to the plane of the triangle. (Each rod has mass $M$ and length $L$)