If you mean electrolysis, its the breaking down or separating of certain compounds or elements, (separating substances in a compound ie , magnesium, lead etc
The chemical decomposition reaction, is made by passing an electrical current through the substance containing ions. But only certain elements/compounds canbe separated using electrolysis, as others are separated using displaysion- (i think that's how u spell it!!.)
Which is when a more reactive or less reactive substance is added to the mixture.
Hope I've helped!!