Chemistry · Redox Equilibrium · NEET
NCERT lists exactly four: (1) Combination A + B to C, (2) Decomposition, one compound breaks into two or more parts, (3) Displacement, one element pushes out another (metal or non-metal), and (4) Disproportionation, the same element is oxidised and reduced at the same time. If you can name the type, you already understand the reaction. Memory hook: Come Down, Don't Delay.
No. A combination or decomposition is redox ONLY if some oxidation number changes. For a combination like A + B to C to be redox, at least one of A or B must be a free element (like O2, H2, or a metal). Decomposition of CaCO3 to CaO + CO2 is NOT redox because Ca stays +2, C stays +4, O stays -2 the whole time. This is a very common NEET trap.
They are opposites. Combination joins two or more substances into one (A + B to C), and it is redox if a free element takes part, like C + O2 to CO2. Decomposition splits one compound into two or more pieces (C to A + B), and it is redox if at least one product is a free element, like 2KClO3 to 2KCl + 3O2 (oxygen goes from -2 to 0).
In disproportionation, the SAME element in ONE oxidation state is both oxidised and reduced at the same time. Example: 2Cu+ to Cu2+ + Cu. Here copper starts at +1 and ends both higher (+2) and lower (0). The element must have a middle oxidation state so it can go both up and down. If the element is already in its highest state (like Cl in ClO4-, Cl = +7), it cannot disproportionate.
Ask three quick questions. Do two things become one? Combination. Does one thing break into many? Decomposition. Does one element replace another? Displacement. Does one element go both up and down at once? Disproportionation. Always assign oxidation numbers first; if nothing changes, it is not redox at all (for example BaCl2 + Na2SO4 to BaSO4 + 2NaCl).
Both are displacement redox. In metal displacement, a more reactive metal pushes out a less reactive metal from its compound, like the thermite reaction Cr2O3 + 2Al to Al2O3 + 2Cr. In non-metal displacement, a more reactive non-metal (or hydrogen) is displaced, for example a reactive metal releasing H2 from acid, or Cl2 displacing Br- from bromide. Both involve electron transfer, so both are redox.
Which reaction is NOT a redox reaction?
Which of the following reactions is a metal displacement reaction?
Which of the following reactions are disproportionation reactions? (a) 2Cu+ to Cu2+ + Cu (b) 3MnO4^2- + 4H+ to 2MnO4- + MnO2 + 2H2O (c) 2KMnO4 to K2MnO4 + MnO2 + O2 (d) 2MnO4- + 3Mn2+ + 2H2O to 5MnO2 + 4H+
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Yes. NCERT Class 11 classifies redox reactions into four types: combination, decomposition, displacement, and disproportionation. Displacement is sometimes split into metal displacement and non-metal displacement, but the main list is four.
Combustion is a combination reaction with oxygen, so it is redox. For example C + O2 to CO2: carbon goes from 0 to +4 and oxygen from 0 to -2. All combustion reactions using free O2 are redox.
No. To disproportionate, an element must be able to go both up and down, so it needs a middle oxidation state. An element already at its highest state, like Cl in ClO4- (+7) or N in HNO3 (+5), cannot disproportionate because it cannot go any higher.
It is the reverse of disproportionation. Two different oxidation states of the same element combine to give a single intermediate state. Example: 2MnO4- + 3Mn2+ + 2H2O to 5MnO2 + 4H+, where Mn +7 and Mn +2 both become Mn +4.
In displacement, one element replaces a DIFFERENT element (Zn replaces Cu in ZnSO4). In disproportionation, ONE element changes into two different states of ITSELF at the same time (2Cu+ to Cu2+ + Cu).
