Final answer:
When released in a uniform electric field, the proton gains kinetic energy while the electron loses kinetic energy due to the work done by the electric field.
Step-by-step explanation:
When a proton and an electron are separately placed at rest in the same uniform electric field and released, the energy of each particle will change. The proton, being positively charged, will move in the direction opposite to the electric field and gain kinetic energy. The electron, being negatively charged, will move in the same direction as the electric field and lose kinetic energy. This change in energy occurs due to the work done by the electric field on the charged particles.