Redox reactions are chemical reactions in which oxidation and reduction occur simultaneously. In every redox reaction, one substance loses electrons (oxidation) while another gains electrons (reduction)—these processes are inherently linked, since electrons lost by one species must be gained by another.

Key features of redox reactions:

• The substance that is oxidized gives up electrons and is called the reducing agent.
• The substance that is reduced gains electrons and is called the oxidizing agent.

For example, in the reaction:
Zn + Cu²⁺ → Zn²⁺ + Cu,

• Zinc is oxidized (loses 2 electrons),
• Copper ion is reduced (gains 2 electrons).

Redox reactions are essential in:

• Battery operation (electrochemical cells)
• Metabolism and respiration in living organisms
• Rusting of metals
• Industrial processes like metal extraction and bleaching

They form the basis of countless natural and technological processes, all involving the flow of electrons from one species to another.