Redox reactions can be written as two half-reactions, focusing on the gain or loss of electrons by one of the chemical substances. One half-reaction shows the oxidation while the other shows the reduction. When the two half-reactions are combined, the overall reaction is obtained.The half-reactions can aid in the balancing of redox equations because the number of each element must be balanced as well as the number of electrons gained and lost. What substance is added to balance the hydrogen in a half-reaction?
A. H₂O₂
B. H₂O
C. H⁺
D. H₂

When we are balancing the reaction in an acid medium, hydrogen is balanced using the H⁺ species. This is most likely the intended answer of your question.

When the reaction takes place not in an acid medium, but in an alkaline one, then hydrogen is present as the OH⁻ species. However this option is not given in your question.

Thus the answer is option C).

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