Chemistry · Electrochemistry · NEET
Oxidation is LOSS of electrons. Reduction is GAIN of electrons. Use the hook OIL RIG: Oxidation Is Loss, Reduction Is Gain. Example: Zn -> Zn2+ + 2e- is oxidation, because zinc LOSES 2 electrons. Cu2+ + 2e- -> Cu is reduction, because the copper ion GAINS 2 electrons. If you remember only one line for NEET, remember OIL RIG.
An oxidising agent is the substance that MAKES the other one oxidise. To do that, it must take electrons, so the oxidising agent itself GAINS electrons and is reduced. A reducing agent GIVES electrons, so it itself LOSES electrons and is oxidised. Quick rule: the reducing agent gets oxidised; the oxidising agent gets reduced. They swap fates. Example: in Zn + Cu2+ -> Zn2+ + Cu, Zn is the reducing agent (it is oxidised) and Cu2+ is the oxidising agent (it is reduced).
Because electrons cannot just disappear or appear out of nowhere. If one substance loses electrons, another substance must catch those same electrons. So oxidation (loss) at one place forces reduction (gain) at another place. That is why we call it a redox reaction: reduction + oxidation joined. The number of electrons lost equals the number gained, always.
A redox couple is just the oxidised form and the reduced form of the SAME element written together, like Zn2+/Zn or Fe3+/Fe2+. The oxidised form is written first, then a slash, then the reduced form. In NEET 2023 the correct definition was: 'Both the reduced and oxidised forms involve the same element.' It is one element in two states, sitting side by side.
Disproportionation is when the SAME species is oxidised and reduced at the same time. One part of it goes up in oxidation state, another part goes down. Example asked in NEET 2018: HBrO (bromine in +1) breaks into Br2 (0) and BrO3- (+5) type products - some bromine is reduced, some is oxidised. A species disproportionates only if it can be both oxidised and reduced under the given conditions.
Track the oxidation number. If an element's oxidation number goes UP (more positive), it lost electrons, so it was oxidised. If the oxidation number goes DOWN (more negative), it gained electrons, so it was reduced. Example: in 2Fe3+ + 2I- -> 2Fe2+ + I2, iron goes from +3 to +2 (reduced), and iodine goes from -1 to 0 (oxidised). Watch the numbers, not just the letters.
The correct option for a redox couple is:
Consider the standard reduction potentials for each step of bromine: BrO4- (+1.82 V) -> BrO3- (+1.50 V) -> HBrO (+1.595 V) -> Br2 (+1.0652 V) -> Br-. The species undergoing disproportionation is:
Zinc can be coated on iron to make galvanised iron but the reverse is not possible. It is because:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
OIL RIG is a memory trick: Oxidation Is Loss, Reduction Is Gain - of electrons. It is the fastest way to never mix up the two in NEET.
No. Electrons cannot vanish. If one substance loses electrons (oxidised), another must gain them (reduced). They always come as a pair, which is why we call it redox.
The oxidising agent gets REDUCED. It takes electrons from the other substance, so it gains electrons itself. Its job is to oxidise someone else, but it does the opposite to itself.
No. A redox couple is the oxidised and reduced forms of ONE element, like Cu2+/Cu. Cathode and anode are the two electrodes of a full cell. NEET 2023 marked 'cathode and anode together' as the wrong option.
Every cell reaction is a redox reaction split into two halves: oxidation at the anode and reduction at the cathode. Electrode potential, EMF and cell notation all build on knowing which side loses and which side gains electrons.
