When an apple turns brown after being sliced, it is reacting with the oxygen in the air—a process known as enzymatic browning. Oxidizing vs. Reducing Agents In a redox reaction, the participants play specific roles:
The substance that gains electrons. It causes the other substance to be oxidized (by "stealing" its electrons). oxidization
When iron is exposed to moisture and oxygen, it undergoes oxidation to form iron oxide, or rust. The iron atoms lose electrons to oxygen atoms. When an apple turns brown after being sliced,