2. Which one of the following is a redox reaction?
a. 𝑂2 + 4𝐻+ + 4𝑒- → 2𝐻2𝑂
b. 𝐻2 → 2𝐻+ + 2𝑒-
c. 2𝐻2 + 𝑂2 → 2𝐻2𝑂
d. 𝐶𝑙2 + 2𝑒- → 2𝐶𝑙-
The correct answer is option c. 2H₂ + O₂ → 2H₂O, as it involves both oxidation and reduction occurring simultaneously, defining a complete redox reaction.
Redox Reaction Definition
A redox reaction features electron transfer where one species undergoes oxidation (electron loss, oxidation state increase) and another reduction (electron gain, oxidation state decrease). Half-reactions show only one process, while complete redox reactions balance both.
Option Analysis
Each option undergoes evaluation through oxidation number changes:
| Option | Reaction | Oxidation State Changes | Type |
|---|---|---|---|
| a | O₂ + 4H⁺ + 4e⁻ → 2H₂O | O: 0 to -2 (reduction only) | Reduction half-reaction |
| b | H₂ → 2H⁺ + 2e⁻ | H: 0 to +1 (oxidation only) | Oxidation half-reaction |
| c | 2H₂ + O₂ → 2H₂O | H: 0 to +1 (oxidation); O: 0 to -2 (reduction) | Complete redox reaction |
| d | Cl₂ + 2e⁻ → 2Cl⁻ | Cl: 0 to -1 (reduction only) | Reduction half-reaction |
Only option c shows dual processes, confirming it as the redox reaction.
CSIR NET Exam Tips
For CSIR NET Life Sciences or Chemistry, identify redox by checking both oxidation and reduction in the net equation, not isolated half-cells. Practice balancing via half-reaction method: split, balance atoms/charge, combine. Common pitfalls include mistaking half-reactions for full redox.
