To determine the number of electrons in an oxygen atom that is represented by the symbol [tex]$O^{2-}$[/tex], we must understand a few key points about oxygen and what the symbol [tex]$O^{2-}$[/tex] signifies.
1. Atomic Number and Neutral Atom: The atomic number of oxygen is 8. This means that a neutral atom of oxygen has 8 protons in its nucleus and, consequently, 8 electrons to balance out the positive charge of the protons.
2. Meaning of the [tex]$^{2-}$[/tex] Symbol: The symbol [tex]$O^{2-}$[/tex] indicates that the oxygen ion has gained 2 extra electrons. This is what the "2-" signifies — the ion has 2 more electrons than protons.
3. Calculating Total Electrons: Since a neutral oxygen atom has 8 electrons, if it gains 2 additional electrons, the total number of electrons becomes:
[tex]\[
8 \text{ (original electrons)} + 2 \text{ (extra electrons)} = 10 \text{ electrons}
\][/tex]
Thus, the total number of electrons in an [tex]$O^{2-}$[/tex] ion is 10.
Therefore, the correct answer is:
[tex]\[
\boxed{10}
\][/tex]
