When atoms are reduced, what occurs?

When atoms are reduced, they gain electrons. This process is a fundamental aspect of redox reactions, where reduction is specifically defined as the addition of electrons to an atom or molecule. The gain of electrons often results in a decrease in the oxidation state of the atom, which may also lead to changes in the atom's charge, typically making it more negative.

In biochemical and physiological contexts, reduction plays a crucial role in various metabolic pathways, including cellular respiration and photosynthesis. For example, during the reduction of NAD+ to NADH, electrons are added, allowing NADH to carry energy and electrons within cells.

The other choices, while related to different processes, do not accurately describe the process of reduction. Losing electrons characterizes oxidation, forming bonds typically refers to interactions between atoms or molecules rather than changes in their electrical states, and releasing energy is often associated with exothermic reactions or oxidation processes rather than reduction itself. Thus, the correct understanding of reduction centers on the gaining of electrons.