# Chapter 4 - Sections 4.1-4.9 - Exercises - Review Questions: 19

Oxidation-reduction reactions are reactions in which electrons are transferred form one reactant to the another and the oxidation states of certain atoms are changed. These are also called redox reactions.

#### Work Step by Step

An example is: $Cu_{2}$$_{(s)}$$+O_{2}$$_{(g)} =&gt; 2Cu_{(s)} +SO_{2}$$_{(g)}$

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