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Why can the ion 0^6+ be considered to be  a helium-like ion, and what subatomic particles it is composed of , and how many there are of each.

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Why can the ion 0^6+ be considered to be  a helium-like ion, and what subatomic particles it is composed of , and how many there are of each.

The electronic configuration of oxygen is:

[He] 2s² 2p⁴

so if you remove the outer 2+4 = 6 electrons, you are left with the electronic configuration of Helium. The electrons in O⁶⁺ don't have the same energy they have in helium, however, because the nuclei have different charges: +2 in the case of He, +8 in the case of O.