What process describes how molecules are formed?

The correct choice emphasizes that molecules are formed when atoms join together through interactions involving their outer electron shells, specifically through chemical bonding. Atoms have electrons that occupy various energy levels, with the outermost electrons, known as valence electrons, playing a critical role in bonding.

When atoms combine to form molecules, they often do so by sharing electrons (in covalent bonds) or transferring electrons (in ionic bonds) to achieve a more stable electronic configuration, typically aiming for a full outer shell, which is often achieved through chemical reactions. This process illustrates the fundamental principle of chemical stability, where atoms seek to minimize their energy by attaining a complete valence shell similar to that of noble gases.

In this context, the formation of molecules directly relates to how atoms interact based on their electron configurations, making this option the best choice to describe the process.