Which of the following reactions is a redox reaction?
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Correct answer
B. CuO + H2 → Cu + H2O
Principle or equation
A redox reaction involves a change in oxidation states of elements. Oxidation is loss of electrons (increase in oxidation state), reduction is gain of electrons (decrease in oxidation state).
Why this answer is correct
In CuO + H2 → Cu + H2O, Cu in CuO has oxidation state +2 and is reduced to Cu (0). H in H2 has oxidation state 0 and is oxidized to +1 in H2O. Thus it is a redox reaction. The other reactions are acid-base, precipitation, or decomposition without oxidation state changes.
Example
CuO + H2 → Cu + H2O: Cu goes from +2 to 0 (reduction), H goes from 0 to +1 (oxidation).
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