Oxidation Number
In the compound potassium permanganate, KMnO_4, what is the oxidation state of the manganese atom when potassium is +1 and oxygen is -2?
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About This Question
- Subject
- chemistry
- Chapter
- redox reactions and electrochemistry
- Topic
- oxidation number
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
+7
Oxidation number is a formal charge assigned to an atom assuming all bonds are ionic, and the algebraic sum of oxidation numbers in a neutral molecule must equal zero. In KMnO_4, potassium contributes +1 and each of the four oxygen atoms contributes -2, giving a total of -8 from oxygen. Let the oxidation state of manganese be x. Then +1 + x + (-8) = 0, so x = +7. Manganese therefore achieves its maximum oxidation state, matching its group position, which is why permanganate is such a strong oxidising agent. Option +2 corresponds to the Mn^2+ ion formed when permanganate is reduced in acidic medium, not to KMnO_4 itself. Option +4 corresponds to MnO_2, the product in neutral or faintly alkaline medium. Option +6 corresponds to the manganate ion MnO_4^2-. This is a standard NCERT application of oxidation-number rules. Plausibility check: +7 is the highest possible for a Group 7 element, consistent with manganese using all its valence electrons.
This easy difficulty chemistry question is from the chapter redox reactions and electrochemistry, covering the topic of oxidation number. It appeared in the 2025 exam.
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