Question

A body in uniform velocity has zero acceleration why?

Answer 1

That's actually the definitions.
"Velocity" means the speed and direction of the body's motion. "Uniform" means the speed and direction aren't changing. "Acceleration" means any change in speed or direction of motion.

Answer 2

when the velocity is uniform, the velocity does not change. since acceleration is the rate of change in velocity, the acceleration will be zero when velocity is uniform