Question

State as oxidation or reduction in the given reaction: $O+2e^{-}\to O^{2-}$

Answer 1

Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom, or ion. Reduction is the gain of electrons or a decrease in oxidation state by a molecule, atom, or ion.
Here,
$O+2e^{-}\to O^{2-}$ in this reaction, oxygen atom is getting two electron and form an anion so its a reduction process.