NEET · Chemistry
Teach the redox half of official Unit 7: oxidation/reduction, oxidation number, oxidising/reducing agents and balanced redox equations. The page is a prerequisite for Electrochemistry and must not duplicate cell-potential or conductivity content.
In short
A redox reaction contains simultaneous oxidation and reduction. Assign oxidation numbers, identify which species loses and gains electrons, label the reducing and oxidising agents, and balance atoms plus charge in the stated medium. The oxidising agent is itself reduced; the reducing agent is itself oxidised.
Oxidation is an increase in oxidation number and loss of electrons; reduction is a decrease in oxidation number and gain of electrons. These changes occur together.
For Fe2+ -> Fe3+ + e-, Fe is oxidised. For Ce4+ + e- -> Ce3+, Ce is reduced. Combining gives the balanced ionic reaction Fe2+ + Ce4+ -> Fe3+ + Ce3+.
A free element has oxidation number 0; a monatomic ion equals its charge; fluorine is -1 in compounds; oxygen is usually -2 with known exceptions such as peroxides; hydrogen is usually +1 with nonmetals and -1 in many metal hydrides. The sum of oxidation numbers equals the species charge. Classify exceptional compound type before applying a default rule.
In acidic medium:
A balanced example is MnO4^- + 8H+ + 5Fe2+ -> Mn2+ + 4H2O + 5Fe3+.
For basic medium, a safe workflow is to first obtain a balanced acidic form, then add OH- to both sides to neutralise residual H+, cancel water where possible, and recheck total charge. Do not merely substitute OH- for H+.
oxidation number rises -> oxidation: Compare same element before/after. Electron loss consistent
oxidation number rises -> oxidation
Use when — Electron loss consistent
oxidation number falls -> reduction: Same element. Electron gain consistent
oxidation number falls -> reduction
Use when — Electron gain consistent
Fe2+ + Ce4+ -> Fe3+ + Ce3+: Aqueous ionic form. atoms/charge balanced
Fe2+ + Ce4+ -> Fe3+ + Ce3+
Use when — atoms/charge balanced
MnO4^- + 8H+ + 5Fe2+ -> Mn2+ + 4H2O + 5Fe3+: Acidic medium. 5 e transfer; atoms/charge balanced
MnO4^- + 8H+ + 5Fe2+ -> Mn2+ + 4H2O + 5Fe3+
Use when — 5 e transfer; atoms/charge balanced
Original NEET-style item: In acidic solution, MnO4^- + 8H+ + 5Fe2+ -> Mn2+ + 4H2O + 5Fe3+. Identify the oxidising agent, reducing agent and electron count transferred per permanganate ion.
Reasoning: Mn changes +7 to +2, gaining 5 electrons, so permanganate is reduced and is the oxidising agent. Each Fe2+ loses one electron to become Fe3+, so Fe2+ is the reducing agent. Five Fe2+ supply the 5 electrons accepted per MnO4^-.
Cannot connect oxidation number with electron transfer
Knowledge gapWhy it happens
Preparation Intelligence classification: Knowledge Gap.
How it is corrected
Write both changes explicitly.
Forgets oxidation-number defaults/exceptions
Recall gapWhy it happens
Preparation Intelligence classification: Recall Gap.
How it is corrected
Retrieve rule with exception cue.
Balances atoms but not charge
Execution errorWhy it happens
Preparation Intelligence classification: Execution Error.
How it is corrected
Run final charge audit.
Selects oxidising agent because it contains oxygen
Decision / selection errorWhy it happens
Preparation Intelligence classification: Decision / Selection Error.
How it is corrected
Identify which species is reduced.
Reaction medium/product is unclear
Needs reviewWhy it happens
Preparation Intelligence classification: Needs Review.
How it is corrected
Do not force a memorised equation without condition.
FAQ
Straight answers about how Rank Sarthi fits into serious exam preparation.
The species that is reduced by gaining electrons and thereby oxidises the other species.
Check every atom, total charge and equality of electrons lost/gained.
Not automatically; balancing and sometimes product form depend on medium.
Official scope is taken from the NEET (UG) 2026 syllabus and official NTA documents; concept structure follows current NCERT contents. No performance, weightage or question-frequency data is asserted.
