Question

Which ion has the most shells that contain electrons??

Answer 1

Maybe the ion from the element Tennessine, `Ts^-`

Explanation:

In 2016 IUPAC announced the new name tennessine (Ts) for element 117 in place of the temporary systematic name (Uus). As you can see `Ts` is really young.
We can not for sure say that the teoretical ion `Ts^-` has the most shells with electrons but if this ion would exist his configuration for the ion would be the same as for the last element in the periodic table, Oganesson- `Og`.
If an atoms gains electrons, it develops a negative charge and becomes an anion and his last shell contains more electrons [as seen on the example below with Fluorine, `F`].

If the element `Ts` would gain electrons his charge will be negative and his ion would look something like this:

In the last shell is the gained electron circled with the blue "marker". Now the ion `Ts^-` has the same electronic configuration as Oganesson , `Og` [the last element in the PSE]

You may have noticed that I have used the word "maybe" and "probably" in my answer and explanation. This is because the "new" element has predicted properties, as seen below.