Number of outer rings in cesium and magnesium? ?

What do you mean outer rings. There is only one OUTER ring in each element. the number of shells varies. Magnesium in its ground state would have electrons in 3 energy levels, filled up to the 3s^2 shell. Caesium would have 6 energy levels filled up to 6s^1

There is only one outer electron shell.
Since magnesium has 12 electrons it has 2 electrons in the outer shell.
Since caesium has 55 electrons it has 1 electron in its outer shell.
Hope this helped in the end because this didn't make sense to me :(