A comproportionation reaction is one where the same element in two different oxidation states (one higher, one lower) reacts to form a single product with an oxidation state in between. It is the exact reverse of disproportionation. Memory hook: "Come together" - two different states of one element COME together into one middle state.
Comproportionation: manganese in +7 and +2 states come together to form a single middle +4 state. Disproportionation is the reverse - one middle state splits into a higher and a lower state.
Your doubts, answered
Is comproportionation the reverse of disproportionation?
Yes, exactly. In disproportionation, ONE element in ONE middle oxidation state splits into a higher and a lower state. In comproportionation, that same element in a HIGH state and a LOW state combines back into a single MIDDLE state. So if you reverse the arrow of a disproportionation reaction, you get a comproportionation reaction.
Give a clear NEET example of comproportionation.
A common one is: 2 MnO4^- (Mn is +7) + 3 Mn^2+ (Mn is +2) + 2 H2O -> 5 MnO2 (Mn is +4) + 4 H^+. Here manganese starts in two different states, +7 and +2, and both end up as +4 in MnO2. Another example: 5 I^- (-1) + IO3^- (+5) + 6 H^+ -> 3 I2 (0) + 3 H2O, where iodine at -1 and +5 meets at 0.
Why is comproportionation still a redox reaction?
Because electrons are transferred between the two forms of the same element. The atom in the higher oxidation state is reduced (gains electrons) and the atom in the lower oxidation state is oxidised (loses electrons). Both the oxidising agent and reducing agent are the SAME element, just in different starting states - so it fits the OIL RIG definition of a redox reaction.
How do I spot comproportionation in an exam?
Look at the reactant side: if you see the SAME element appearing in TWO different oxidation states, and on the product side that element is in ONE single intermediate state, it is comproportionation. If instead one state on the left becomes two states on the right, it is disproportionation.
⚠️ The NEET trap ✗ Treating 2MnO4^- + 3Mn^2+ + 2H2O -> 5MnO2 + 4H^+ as a disproportionation reaction. ✓ It is COMPROPORTIONATION. Two different states of Mn (+7 and +2) MERGE into one middle state (+4). Disproportionation is the opposite: one state splits into two. 🧠 On the reactant side, count the oxidation states of the repeated element. TWO different states merging into ONE = comproportionation. ONE state splitting into TWO = disproportionation.
Real NEET questions
2019
Which of the following reactions are disproportionation reactions? (a) 2Cu+ -> Cu2+ + Cu (b) 3MnO4^2- + 4H+ -> 2MnO4- + MnO2 + 2H2O (c) 2KMnO4 -> K2MnO4 + MnO2 + O2 (d) 2MnO4- + 3Mn2+ + 2H2O -> 5MnO2 + 4H+
A · (a) and (b) only ✓
B · (a), (b) and (c)
C · (a), (c) and (d)
D · (a) and (d) only
Solution: In (a) Cu+ splits into Cu2+ and Cu, and in (b) Mn+6 splits into Mn+7 and Mn+4 - both are disproportionation. Reaction (d) is the trap: Mn+7 and Mn+2 MERGE into Mn+4, so it is COMPROPORTIONATION, not disproportionation. Reaction (c) also involves oxygen change, so it is not a pure single-element disproportionation. Hence only (a) and (b), option A.
Solved Redox Equilibrium NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is a redox reaction where an element in a high oxidation state and the same element in a low oxidation state combine to give a single intermediate oxidation state.
What is another name for comproportionation?
It is also called synproportionation. Both names describe the reverse of disproportionation.
Is comproportionation important for NEET?
Yes. NEET often mixes one comproportionation reaction into a list of disproportionation reactions as a trap (as in 2019). Knowing the difference lets you eliminate the wrong option instantly.
Do both the oxidising and reducing agent have to be the same element?
Yes. That is the defining feature - the same element provides both the species being oxidised and the species being reduced.
