Which of the following chemical equations represents a redox reaction?
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Correct answer
C. 2KClO3(s) → 2KCl(s) + 3O2(g)
Principle or equation
A redox reaction involves a change in oxidation states of some elements. Oxidation is loss of electrons (increase in oxidation number), reduction is gain of electrons (decrease in oxidation number). In the decomposition of potassium chlorate, chlorine is reduced from +5 to -1 and oxygen is oxidized from -2 to 0.
Why this answer is correct
In 2KClO3(s) → 2KCl(s) + 3O2(g), the oxidation number of Cl changes from +5 in KClO3 to -1 in KCl (reduction), and O changes from -2 in KClO3 to 0 in O2 (oxidation). Thus, it is a redox reaction. The other reactions are metathesis (double displacement) or acid-base reactions with no oxidation state changes.
Example
In the reaction 2H2O2(aq) → 2H2O(l) + O2(g), oxygen is both oxidized and reduced (disproportionation), so it is a redox reaction.
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