Q10 / 90 · JEE Main 2024 (01 Feb Shift 1) · Chemistry

Which of the following reactions are disproportionation reactions?

1 Cu+→Cu2++Cu

2 3MnO42-+4H+→2MnO4-+MnO2+2H2O

3 2KMnO4→K2MnO4+MnO2+O2

4 2MnO4-+3Mn2++2H2O→5MnO2+4H+

Choose the correct answer from the options given below:

  • Correct answer
    A
    1, 2
  • B
    2, 3, 4
  • C
    1, 2, 4
  • D
    1, 4

Solution

In disproportionation reaction,  both oxidation and reduction of same chemical species occurs.

  • Oxidation is gain in oxidation number.
  • Reduction is loss in oxidation number.

1) Cu+⟶Cu2++Cu

Oxidation state of Cu+=+1.

Oxidation state of Cu2+=+2.

Oxidation state of Cu=0 .

Here, Cu+ is getting both reduced and oxidised.

2) 3MnO4-+4H+⟶2MnO4-+MnO2+2H2O

Oxidation state of Mn in MnO4-=+7.

Oxidation state of Mn in MnO2 =+4.

Here, reduction is taking place.

3) 2KMnO4⟶K2MnO4+MnO2+O2

Here in the reaction, Mn is changing its oxidation state from +7 to +6 and +4. In both cases, reduction is occurring.

4) 2MnO4-+3Mn2++2H2O⟶5MnO2+4H+

Here in the reaction, product with Mn in only one, so there is no possibility of both oxidation and reduction reactions at the same time.

Hence, the correct answer is option: 'A'.

Relevant Questions