The concept of an electron in its "highest orbital" and "leaving the atom" refers to the ionization process, where an electron gains sufficient energy to overcome the attractive force of the atomic nucleus and becomes unbound from the atom. The velocity of an electron in this state can vary, depending on the specific circumstances.
However, it's important to note that in the context of quantum mechanics, the behavior of electrons is described by wave functions rather than classical trajectories. Therefore, talking about the velocity of an electron in its highest orbital just before leaving the atom may not be meaningful in the traditional sense of velocity.
In the context of ionization, the energy of the electron is more commonly discussed. The energy required to remove an electron from an atom is called the ionization energy, and it varies depending on the atom and its electronic configuration. When an electron gains enough energy to surpass the ionization energy, it can be ejected from the atom. The energy gained by the electron can be converted into kinetic energy, but it is not described in terms of a classical velocity.
If you provide more information about the specific atom or system you are interested in, I can try to provide more details on the ionization process and the energy involved.