Sodium, with an atomic number of 11, has 11 electrons. To achieve a stable electron configuration, sodium can lose one electron.
By losing one electron, sodium forms a positive ion (cation) with a charge of +1. The resulting sodium ion (Na+) will have 10 electrons, which corresponds to the electron configuration of the noble gas neon (with an atomic number of 10).
This electron loss allows sodium to achieve a more stable electron configuration by having a completely filled outermost electron shell, which is desirable for greater stability.