Why is it that when something gains electrons, it is said to be reduced? What is being reduced?

Oxidation and reduction are two processes that are part of redox (reduction-oxidation) reactions in chemistry. In a redox reaction, one reactant gets oxidized (loses electrons), while the other reactant gets reduced (gains electrons). These two processes occur simultaneously.

In a redox reaction, reduction is the process where a species gains electrons. When a species gains electrons, its overall charge is reduced due to the additional negative charges. The term "reduction" implies a decrease in oxidation state, indicating that the species involved has lost positive charge (become less positive) during the reaction.

When we say that something gains electrons and is being reduced, we are referring to the oxidizing agent in the reaction. The oxidizing agent accepts electrons from another species and is thus reduced. Conversely, the reducing agent loses electrons and is oxidized. In any redox reaction, both processes (oxidation and reduction) occur simultaneously. For example, for a redox reaction between hydrogen (H) and oxygen (O) to form water (H2O), the reaction can be represented as: \[ 2H_2 + O_2 \rightarrow 2H_2O \] In this redox reaction, hydrogen is being oxidized (losing electrons and becoming more positive) to form water. Oxygen, on the other hand, is being reduced (gaining electrons and becoming less positive), also forming water. In this case, what is being reduced is the oxygen molecule (O2).