Answer:
Outer
Explanation:
If you take a look at all atoms you can see that for example Na is in the first group and has 1 electron in its last shell.
It has 11 electrons. 2 electron go in the first shell, 8 in the 2. shell and one electron is left in the 3. shell (which is also why it reacts well) you can look at all atoms it might work every where.