Answer:
2. Redox
Explanation:
A redox reaction is that in which an element is reduced while another element is oxidized. For example, let's consider the following redox reaction.
Fe + S ⇒ FeS
Fe is oxidized because it loses electrons to form Fe²⁺, while its oxidation number increases from 0 to 2+.
S is reduced because it gains electrons to form S²⁻, while its oxidation number decreases from 0 to 2-.
