A charged particle describes a circle under the influence of the magnetic field. The quantities that remain constant are
i) K. E 
ii) Velocity
iii) Time period 
iv) Momentum

Magnetic force can not change the speed of the particle moving in the magnetic field. So, the kinetic energy will be constant.

Direction changes throughout the motion, so, velocity and momentum changes.

Time period is calculated as,

$\mathrm{T}=\frac{2\mathrm{\pi m}}{\mathrm{qB}}$

So, time period will not change for a charged particle moving in a uniform magnetic field.