When a 3s electron becomes a 2s electron, it undergoes a transition from a higher energy state (3s) to a lower energy state (2s). This transition is accompanied by the release of energy, which is emitted in the form of a photon of light. The energy of the photon is equal to the energy difference between the 3s and 2s orbitals.

The transition from 3s to 2s is a forbidden transition in atomic physics, meaning that it is not allowed by the selection rules for atomic transitions. However, it can occur in certain circumstances, such as when the atom is in a highly excited state or when it is in a strong electric or magnetic field.

When the 3s electron becomes a 2s electron, the atom undergoes a change in its electronic configuration. The 3s orbital becomes empty, while the 2s orbital becomes occupied by two electrons. This change in electronic configuration can affect the atom's properties, such as its chemical reactivity and its magnetic properties.

Overall, the transition of a 3s electron to a 2s electron is a process that involves the release of energy and a change in the atom's electronic configuration.