Rotational Mechanics Questions

For a given uniform square lamina $ABCD$ with centre $O$, let $I_{AC}$ and $I_{EF}$ be the moments of inertia about the diagonal $AC$ and the line $EF$ passing through $O$ and parallel to side $AB$ respectively. Then:

A round uniform body of radius $R$, mass $M$ and moment of inertia $I$, rolls down (without slipping) an inclined plane making an angle $\theta$ with the horizontal. Then its acceleration is:

Angular momentum of a particle rotating with a central force is constant due to: