What is added to balance hydrogen and oxygen atoms in an oxidation-reduction reaction in basic solution?

In an oxidation-reduction reaction in basic solution, hydroxide ions (OH⁻) are added to balance the hydrogen atoms. After balancing the half-reactions for mass and charge, any excess hydrogen ions (H⁺) are neutralized by adding an equal amount of hydroxide ions, forming water. This ensures that both hydrogen and oxygen atoms are balanced in the overall reaction.