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Which of these half-reactions represents reduction?

I. Fe2+ → Fe3+
II. Cr2O72- → Cr3+
III. MnO4- → Mn2+

1 Answer

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Answer: The half-reactions represents reduction are as follows.


  • Cr_(2)O^(2-)_(7) \rightarrow Cr^(3+)

  • MnO^(-)_(4) \rightarrow Mn^(2+)

Step-by-step explanation:

A half-reaction where addition of electrons take place or a reaction where decrease in oxidation state of an element takes place is called reduction-half reaction.

For example, the oxidation state of Cr in
Cr_(2)O^(2-)_(7) is +6 which is getting converted into +3, that is, decrease in oxidation state is taking place as follows.


Cr_(2)O^(2-)_(7) + 3 e^(-) \rightarrow Cr^(3+)

Similarly, oxidation state of Mn in
MnO^(-)_(4) is +7 which is getting converted into +2, that is, decrease in oxidation state is taking place as follows.


MnO^(2-)_(4) + 5 e^(-) \rightarrow Mn^(2+)

Thus, we can conclude that half-reactions represents reduction are as follows.


  • Cr_(2)O^(2-)_(7) \rightarrow Cr^(3+)

  • MnO^(-)_(4) \rightarrow Mn^(2+)
User Florian Greinacher
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