What does reduction refer to in terms of electron transfer and oxidation number?

Reduction refers to a process in which a species gains electrons. This gaining of electrons results in a decrease in oxidation number. When an atom or molecule gains electrons, its oxidation state is reduced, indicating that it has become more negatively charged. This concept is essential in redox (reduction-oxidation) reactions, where the transfer of electrons occurs between different species.

In redox reactions, reduction is always accompanied by oxidation, which is the loss of electrons and an increase in oxidation number. The interplay between these two processes allows for the transfer of energy and the formation of compounds. Understanding the link between electron transfer and changes in oxidation state is crucial for predicting and explaining chemical reactivity.