In the case of uniform circular motion,which of the following physical quantities does not remain constant?

If the speed $(v)$ and radius $(r)$ of a particle performing uniform circular motion are both doubled,find its new centripetal acceleration.

If a body moving in a circular path maintains a constant speed of $10 \,ms^{-1}$, then which of the following correctly describes the relation between acceleration $(a)$ and radius $(r)$?

$A$ particle is moving along a circle such that it completes one revolution in $40 \, s$. In $2 \, \text{minutes} \, 20 \, s$, the ratio $\frac{|\text{displacement}|}{\text{distance}}$ is:

$A$ particle is moving with constant speed in a circular path. When the particle turns by an angle $90^{\circ}$,the ratio of instantaneous velocity to its average velocity is $\pi : x \sqrt{2}$. The value of $x$ will be $.........$

"$A$ particle moving with constant speed on a circle about a fixed axis has a constant angular velocity,but its linear velocity is not constant." Is this possible? Why?