Chemistry · Redox Equilibrium · NEET
It is one reaction where two things happen together: one atom loses electrons (oxidation) and another atom gains electrons (reduction). "Redox" is just "reduction" + "oxidation" joined. Example: Zn + CuSO4 -> ZnSO4 + Cu. Here Zn loses electrons (0 to +2) and Cu gains them (+2 to 0). Both happen in the same reaction, so it is redox.
No. Electrons cannot vanish. If one atom loses electrons, another atom must gain those exact electrons. So oxidation and reduction always come as a pair. This is the whole idea of the word "redox". For NEET, if you find an atom whose oxidation number went up, some other atom's oxidation number must have gone down.
Find the oxidation number of every element on both sides. If at least one element's oxidation number CHANGES, it is a redox reaction. If no element changes its oxidation number, it is NOT redox (it is something like double displacement, acid-base, or precipitation). This one check is the fastest way to answer NEET questions.
Because no atom changes its oxidation number. Ba stays +2, Cl stays -1, Na stays +1, S stays +6, O stays -2 on both sides. The ions just swap partners. This is a double-displacement (precipitation) reaction, not redox. NEET loves to hide one such non-redox option among redox ones.
Most combination, decomposition, and displacement reactions ARE redox because oxidation numbers change (like Zn + CuSO4, or H2 + Cl2 -> 2HCl). But double-displacement reactions (partner swaps like BaCl2 + Na2SO4) are usually NOT redox because no oxidation number changes. Always confirm by checking oxidation numbers, never by name alone.
A redox couple is the oxidised form and the reduced form of the SAME element written together, like Cu2+/Cu or Fe3+/Fe2+. Both forms have the same element in two different oxidation states. NEET 2023 asked exactly this: the correct definition is "both the reduced and oxidised forms involve the same element."
Which reaction is NOT a redox reaction?
What is the change in oxidation number of carbon in the reaction CH4(g) + 4Cl2(g) -> CCl4(l) + 4HCl(g)?
The correct option for a redox couple is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Yes. That is the definition. Electrons lost by one atom must be gained by another atom, so oxidation and reduction always happen together in the same reaction.
"Oxidation" and "reduction" describe what one atom does (lose or gain electrons). "Redox" is the whole reaction that contains both at once. You cannot have real oxidation in a reaction without reduction somewhere else in it.
Assign oxidation numbers to all elements on both sides. If any oxidation number changes, it is redox. If none change, it is not redox. This works for every NEET question on this topic.
Redox is the base for the whole chapter: oxidising and reducing agents, balancing equations, KMnO4 and K2Cr2O7 reactions, disproportionation, and electrode potentials. Almost every year NEET asks at least one "which is/ is not redox" or oxidation-number question, so mastering this saves easy marks.
