rotational mechanics Questions

Let $\vec{F}$ be the force acting on a particle having position vector $\vec{r}$ and $\vec{\tau }$ be the torque of this force about the origin. Then:

A particle performing uniform circular motion has angular momentum $L$. If its angular frequency is doubled and its kinetic energy halved, then the new angular momentum is:

A circular disc $X$ of radius $R$ is made from an iron plate of thickness $t$, and another disc $Y$ of radius $4R$ is made from an iron plate of thickness $t/4$. The relation between the moment of inertia $I_X$ and $I_Y$ is: