[tex]\qquad\qquad\huge\underline{{\sf Answer}}♨[/tex]
The ion had 4+ charge when it had 86 electrons, so it should have no charge on it if there are 4 more electrons and the atom will be neutral.
And since we know that number of electrons in a neutral atom is equal to Atomic Number of that atom.
So, at neutral phase, it had 86 + 4 = 90 electrons
hence, our required atom is : Thorium
And it's ion will be ~[tex]\sf Th^{4+} [/tex]
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