* Alkali Metals: Alkali metals are in Group 1 of the periodic table. They have one valence electron.

* Stable Ion: A stable ion has a full outer shell of electrons. This usually means it has the same number of electrons as a noble gas.

* 86 Electrons: 86 electrons is the number of electrons in the noble gas radon (Rn).

Therefore, the alkali metal whose most stable ion contains 86 electrons is Francium (Fr).

Here's why:

* Francium has 87 protons and, in its neutral state, 87 electrons.

* When Francium loses its one valence electron, it becomes a positively charged ion (Fr+).

* This ion now has 86 electrons, the same number as radon.