Question

what is the symbol for the ion that forms when oxygen gains two electrons? o+2e−→ o²− o²+ o₂−

Explanation:

When an atom gains electrons, it forms a negatively - charged ion (anion). Oxygen ($O$) has 6 valence electrons. Gaining 2 electrons gives it a full outer shell (8 electrons). The charge on the ion is determined by the number of electrons gained. Since it gains 2 electrons, the charge is - 2. The symbol for the oxygen atom is $O$, and when it gains 2 electrons, the ion symbol is $O^{2 - }$. The option $O^{2+}$ is incorrect because it implies losing 2 electrons (which would make it a cation, but oxygen typically gains electrons to achieve a stable configuration). The option $O_{2 - }$ is incorrect as the subscript 2 would imply 2 oxygen atoms, but here we are dealing with a single oxygen atom gaining electrons.

Answer:

$O^{2 - }$ (the first option)