Which particle is gained and lost during a redox process?

electrons

Explanation:

A redox reaction is one in which oxidation and reduction takes place. in the sense of

oxidation being the loss of electrons and reduction the gain of electrons.

the old alchemists made significant contributions to science even though there starting premises were off a bit. their conclusions after failure would steer them into better directions for investigation. science is no more than close observation and the initial mistakes result in rethinking and retrying experiments.