Question

Name a physical quantity that (a) varies (b) remain same in the uniform circular motion

Answer 1

as the name suggests uniform circular motion is a type of motion in which speed of the object moving in that circular motion remains constant soyou got the answer of a part that is speed remains constant
so now let's answer about what is the quantity that is variable in uniform circular motion
it is velocity
don't get confused here you must be clear about the difference between speed and velocity simply remember speed is simply a magnitude or scalar quantity where is Velocity includes magnitude as well as direction and as you can see in my picture which I have posted with this answer showing direction of speed at every point is changing( showm by tangents ) so its velocity will be variable hope you got it