Free Balancing Redox Equations MCQs with Answers

1. When balancing a redox equation by the ion electron method, the two half equations must be multiplied so that

• A. the number of atoms of oxygen is the same in both
• B. the number of electrons lost equals the number gained
• C. the charges on both sides are zero
• D. the coefficients are all whole numbers greater than one

Explanation: Electrons cannot appear in the final equation, so the two half equations are scaled until the electrons cancel exactly on addition, which is simply a statement that charge is conserved. Oxygen and hydrogen are balanced separately by adding water and hydrogen ions in acidic solution. The total charge on each side need not be zero, only equal.

2. In balancing a redox equation in acidic medium, oxygen atoms are balanced by adding

• A. hydroxide ions
• B. oxygen gas
• C. water molecules to the side deficient in oxygen
• D. hydrogen gas

Explanation: Water supplies the missing oxygen, and hydrogen ions are then added to the opposite side to balance the hydrogen introduced, which is valid because both are abundant in an acidic solution. In alkaline medium hydroxide ions are used instead, since hydrogen ions cannot be present in quantity. Adding elemental oxygen or hydrogen would change the chemistry rather than balance the equation.