NEET · Chemistry
Own official Unit 11: first-row transition electronic configurations and trends, colour/magnetism/complex formation/catalysis/interstitial compounds/alloys, preparation/properties of K2Cr2O7 and KMnO4, plus lanthanoid/actinoid concepts including contraction and oxidation states.
In short
Use the ionic electronic configuration first, then infer d-electron count, unpaired electrons and likely magnetic behaviour. Transition-element chemistry shows variable oxidation states, colour, complex formation and catalysis. Dichromate and permanganate equations must state reaction medium because their reduction products and electron counts depend on conditions.
A useful general d-block pattern is (n-1)d1-10 ns0-2, with recognised atom-level exceptions. For ions, remove electrons according to the correct ionisation sequence before counting d electrons.
First-row transition scope includes variable oxidation state, ionic radius, colour, catalytic behaviour, magnetism, interstitial compounds, alloys and complex formation.
At the basic spin-only level, mu=sqrt(n(n+2)) BM, where n is number of unpaired electrons. This is a model for appropriate paramagnetic ions; do not extend it to situations requiring advanced orbital contributions.
A balanced chromite-to-chromate roasting equation is: 4FeCr2O4 + 8Na2CO3 + 7O2 -> 8Na2CrO4 + 2Fe2O3 + 8CO2.
Acidification: 2Na2CrO4 + H2SO4 -> Na2Cr2O7 + Na2SO4 + H2O.
Conversion: Na2Cr2O7 + 2KCl -> K2Cr2O7 + 2NaCl.
Acidic reduction half-reaction: Cr2O7^2- + 14H+ + 6e- -> 2Cr3+ + 7H2O.
Representative manganate formation: 2MnO2 + 4KOH + O2 -> 2K2MnO4 + 2H2O.
One conversion route: 3K2MnO4 + 2H2O -> 2KMnO4 + MnO2 + 4KOH.
Acidic reduction: MnO4^- + 8H+ + 5e- -> Mn2+ + 4H2O.
Neutral/mildly basic reduction toward MnO2: MnO4^- + 2H2O + 3e- -> MnO2 + 4OH-.
Lanthanoid contraction is the gradual size decrease across the lanthanoids as increasing nuclear charge is imperfectly shielded by 4f electrons. Actinoids show a wider oxidation-state range because relevant 5f, 6d and 7s levels can be close in energy. Keep depth aligned to current NCERT/NEET.
mu=sqrt(n(n+2)) BM: Spin-only model; n unpaired electrons. Count after ionic d configuration
mu=sqrt(n(n+2)) BM
Use when — Count after ionic d configuration
Cr2O7^2- +14H+ +6e- ->2Cr3+ +7H2O: Acidic. atoms/charge balanced
Cr2O7^2- +14H+ +6e- ->2Cr3+ +7H2O
Use when — atoms/charge balanced
MnO4^- +8H+ +5e- ->Mn2+ +4H2O: Acidic. Mn +7 to +2
MnO4^- +8H+ +5e- ->Mn2+ +4H2O
Use when — Mn +7 to +2
MnO4^- +2H2O +3e- ->MnO2 +4OH-: Neutral/mild basic. Mn +7 to +4
MnO4^- +2H2O +3e- ->MnO2 +4OH-
Use when — Mn +7 to +4
Chromite roasting equation: Oxidising alkaline roast. atom-balanced
Chromite roasting equation
Use when — atom-balanced
Original NEET-style item: Mn is [Ar]3d5 4s2. For Mn2+, use the basic high-spin free-ion count to find unpaired electrons and spin-only magnetic moment.
Reasoning: Remove two 4s electrons: Mn2+=[Ar]3d5. The five d orbitals are singly occupied, so n=5. mu=sqrt(5(7))=sqrt35=5.92 BM approximately.
Cannot derive d count after ionisation
Knowledge gapWhy it happens
Preparation Intelligence classification: Knowledge Gap.
How it is corrected
Build neutral -> ion electron-removal sequence.
Forgets medium-dependent MnO4 products
Recall gapWhy it happens
Preparation Intelligence classification: Recall Gap.
How it is corrected
Retrieve medium/product/electron count together.
Counts unpaired electrons from neutral atom
Execution errorWhy it happens
Preparation Intelligence classification: Execution Error.
How it is corrected
Write ionic configuration first.
Uses memorised oxidant equation without medium
Decision / selection errorWhy it happens
Preparation Intelligence classification: Decision / Selection Error.
How it is corrected
Identify medium before choosing half-reaction.
Preparation condition/exception uncertain
Needs reviewWhy it happens
Preparation Intelligence classification: Needs Review.
How it is corrected
Verify against NCERT/source.
FAQ
Straight answers about how Rank Sarthi fits into serious exam preparation.
Their ns and (n-1)d electrons can be close enough in energy that different counts participate depending on element/environment.
mu=sqrt(n(n+2)) BM.
The reduction product and electron count differ between acidic and neutral/basic conditions.
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.
