Complete Inorganic Chemistry Last 15 Years PYQs Concept Revision For NEET

Inorganic Chemistry questions in NEET often test direct NCERT facts, making this section one of the most scoring parts of the Chemistry paper. Along with these, students regularly face questions on periodic trends, electronic configuration, molecular structure, coordination compounds, and oxidation-reduction concepts.

Previous-year questions help identify repeated patterns and the topics that NEET returns to again and again. However, preparation should remain limited to the current syllabus and reliable NCERT-based concepts, so that revision stays focused and accurate.

Periodic Trends And Electronic Configuration

Periodic trends and electronic configuration form the base of NEET Inorganic Chemistry, as many questions on size, ionisation enthalpy, electronegativity and magnetic behaviour depend on them. Learn the key orders and exceptions below, since the same patterns return in PYQs year after year.

Isoelectronic Species And Ionic Size

Isoelectronic species contain the same number of electrons. Their size depends mainly on nuclear charge.

For isoelectronic species:

• Higher positive charge gives a smaller radius.

• Higher negative charge gives a larger radius.

• Cations are smaller than their neutral atoms.

• Anions are larger than their neutral atoms.

The important order is:

Al3+ < Mg2+ < Na+ < F- < O2- < N3-

For ions of the same element:

M3+ < M2+ < M+ < M < M- < M2- < M3-

Memory Tip: More positive charge means smaller radius, while more negative charge means larger radius.

Ionisation Enthalpy Exceptions

The second-period increasing order is:

Li < B < Be < C < O < N < F < Ne

Two exceptions are important:

• Boron has lower ionisation enthalpy than beryllium because its removed electron is in a higher-energy 2p orbital.

• Oxygen has lower ionisation enthalpy than nitrogen because nitrogen has the stable half-filled 2p3 configuration.

Memory Tip: Remember, “B comes before Be, and O comes before N” in increasing ionisation enthalpy.

Electronegativity

On the Pauling scale:

N < O < F

Fluorine has the highest electronegativity. Nitrogen and chlorine do not have equal electronegativity values.

Important Electronic Configurations

• Fe: [Ar] 3d6 4s2

• Fe2+: [Ar] 3d6

• Fe2+ therefore contains six d-electrons.

• Sc3+ is d0 and diamagnetic.

• Cu+ is d10 and diamagnetic.

Electrons are removed from the 4s orbital before the 3d orbital during transition-metal ion formation.

Chemical Bonding And Molecular Structure

Chemical bonding and molecular structure decide the shape, polarity and stability of molecules, which makes this one of the most frequently tested areas in NEET Inorganic Chemistry. Focus on bond order, dipole moment, bond angles and molecular orbital theory, as PYQs keep returning to these ideas.

Bond Order, Bond Length, And Stability

A bond order of zero indicates that bonding and antibonding effects cancel. Such a species is not stable as a conventional molecule.

The key relationships are:

• Higher bond order gives greater bond strength.

• Higher bond order gives higher bond enthalpy.

• Higher bond order gives greater stability.

• Higher bond order gives shorter bond length.

Thus, for N2, O2, and H2:

Bond strength: N2 > O2 > H2

The reverse order generally applies to bond length.

Dipole Moment And Molecular Polarity

Dipole moment is represented by μ.

• μ = 0 indicates a nonpolar molecule.

• μ not equal to 0 indicates a polar molecule.

• Molecular symmetry can cancel individual bond dipoles.

Examples:

• BF3 is trigonal planar and nonpolar because three equal bond dipoles cancel.

• BeF2 and CO2 are linear and nonpolar.

• CCl4 is symmetrical and nonpolar.

• CHCl3 is polar because all surrounding atoms are not identical.

• PCl5 is nonpolar when all five surrounding atoms are chlorine.

For p-dichlorobenzene, the two C–Cl bond dipoles oppose each other and cancel.

NH3 And NF3 Dipole Moments

The dipole moment of NH3 is greater than that of NF3.

In NH3, the N–H bond dipoles and the lone-pair contribution reinforce each other. In NF3, the N–F bond dipoles oppose the lone-pair contribution.

Memory Tip: In NH3, dipoles reinforce; in NF3, dipoles oppose. Therefore, μ of NH3 is greater than μ of NF3.

Lone Pairs And Bond Angles

All CH4, NH3, and H2O have sp3 hybridisation, but their bond angles differ:

The order is:

CH4 > NH3 > H2O

Memory Tip: More lone pairs mean greater repulsion and a smaller bond angle.

The repulsion order is:

Lone pair-lone pair > lone pair-bond pair > bond pair-bond pair

Molecular Orbital Theory

Bonding molecular orbitals form through constructive interference. They increase electron density between nuclei and stabilise the molecule.

Antibonding molecular orbitals form through destructive interference. They reduce electron density between nuclei and weaken the bond.

Sigma orbitals are symmetrical around the internuclear axis. Pi orbitals have electron density above and below the bond axis.

For C2, the molecular-orbital description discussed gives only pi bonding contributions.

P-Block Chemistry

P-block chemistry covers the properties of hydrides, halogens, oxides and allotropes, and it is full of direct NCERT facts that NEET repeats in PYQs. Pay close attention to the trends in boiling point, acidic strength, thermal stability and molecular geometry, as small exceptions often decide the correct answer.

Hydride Trends

Boiling-point trends are affected by hydrogen bonding.

For hydrogen halides:

Boiling point: HF > HI > HBr > HCl

HF has an unusually high boiling point because of strong hydrogen bonding.

Acidic strength increases down the group:

HF < HCl < HBr < HI

Lower pKa means greater acidic strength. Down the group, the H–E bond becomes longer and weaker, so release of H+ becomes easier.

Thermal Stability Of Group 16 Hydrides

Thermal stability decreases down Group 16 because the E–H bond becomes longer and weaker:

H2O > H2S > H2Se > H2Te > H2Po

Fluorine As The Strongest Oxidising Agent

Fluorine is the strongest oxidising agent due to:

• Relatively weak F–F bond strength.

• High hydration stability of the small F- ion.

The less negative electron-gain enthalpy of fluorine compared with chlorine is not the main reason for its strongest oxidising nature.

Interhalogen Geometry

Interhalogen compounds are formed when two different halogens combine, and their shapes follow VSEPR theory based on the number of bond pairs and lone pairs around the central atom. Remember the geometry of each compound below, as NEET often asks it directly.

Important Oxides And Allotropes

Oxides and allotropes are a favourite source of direct NCERT-based questions in NEET, especially on acidic and basic nature, oxidation states and structure. Learn the key examples below, as the same facts are repeated across PYQs.

• Cl2O7 is the anhydride of perchloric acid.

• CrO is basic.

• Cr2O3 is amphoteric.

• Sb2O5 exists; antimony can show both +3 and +5 oxidation states.

• Diamond is sp3-hybridised and has a three-dimensional covalent network.

• Graphite is sp2-hybridised, layered, and used as a dry lubricant.

• Fullerene has a cage-like structure.

Coordination Compounds

Coordination compounds are a high-weightage topic in NEET Inorganic Chemistry, covering ligand strength, magnetic behaviour, hybridisation, naming and isomerism. Understand how ligands affect splitting and electron pairing, as many PYQs are built on this one idea.

Ligand Strength And Magnetic Behaviour

For octahedral d6 complexes:

A strong ligand produces greater crystal-field splitting.

The important spectrochemical trend includes:

• CO and CN- are strong-field ligands.

• NH3 is stronger than H2O.

• F- is stronger than SCN- in the discussed comparison.

Geometry And Hybridisation

The geometry of a coordination compound depends on its coordination number and the type of hybridisation of the central metal ion. Match each coordination number with its hybridisation and shape below, as NEET often asks this directly

XeF4 has octahedral electronic geometry but square-planar molecular shape.

EDTA, Chelation, And Coordination Number

EDTA is hexadentate. It coordinates through two nitrogen and four oxygen donor atoms.

Chelation increases stability because multidentate ligands form rings with the metal centre.

Coordination number counts donor atoms directly bonded to the metal. Ethylenediamine and oxalate are both bidentate ligands.

Isomerism

• Linkage isomerism: different donor atoms of an ambidentate ligand.

• Ionisation isomerism: exchange of ions inside and outside the coordination sphere.

• Hydrate isomerism: different positions of water molecules.

• Coordination isomerism: ligand exchange between coordination spheres.

• Geometrical isomerism: cis and trans arrangements.

• Optical isomerism: non-superimposable mirror-image forms.

Important Naming Rule

For [Fe(CN)6]3-, iron has oxidation state +3:

x + 6(-1) = -3

Therefore, the name is hexacyanidoferrate(III) ion.

Updated IUPAC terminology prefers cyanido, chlorido, and bromido over older forms such as cyano, chloro, and bromo.

Transition And Inner-Transition Elements

Transition and inner-transition elements are tested in NEET Inorganic Chemistry for their magnetic behaviour, variable oxidation states and periodic contractions. Learn the spin-only formula and the key oxidation-state trends below, as these are repeated across PYQs.

Magnetic Moment

The spin-only magnetic moment is:

μ = square root of n(n + 2) BM

Here, n is the number of unpaired electrons.

For d6, d7, and d8 configurations, the number of unpaired electrons is 4, 3, and 2, respectively.

Oxidation-State Trends

• Cr2+ is a reducing agent because it is oxidised to stable Cr3+, which has a d3 configuration.

• Cu+ disproportionates in water:

2Cu+ gives Cu2+ + Cu

• Cu2+ is more stable than Cu+ in aqueous solution because of its greater hydration enthalpy.

• Zinc mainly shows +2 because of its stable d10 configuration.

• Transition metals show catalytic activity because they can adopt variable oxidation states.

Lanthanoid Contraction

Lanthanoid contraction results from the poor shielding ability of 4f electrons. Increasing nuclear charge therefore causes decreasing atomic size.

Zirconium and hafnium have similar sizes due to lanthanoid contraction.

Ce4+ is f0, and Yb2+ is f14; both are diamagnetic.

Additional lanthanoid oxidation states include:

• Eu2+

• Ce4+

• Yb2+

• Tb4+

Memory Tip: “Cinema Gadar Lut Gayi” helps recall important lanthanoids associated with a 5d1 configuration, especially gadolinium.

Actinoid Trends

Actinoids show more variable oxidation states because the energies of their orbitals are comparable. Actinoid contraction is greater than lanthanoid contraction because 5f electrons shield poorly.

Common Mistakes to Avoid in NEET Inorganic Chemistry 

Most marks in NEET Inorganic Chemistry are lost on exceptions, orders and small definitions rather than on difficult concepts. Keep these frequent PYQ traps in mind while revising periodic trends, bonding, coordination compounds and the d- and f-block:

• Ionisation enthalpy order: Writing Li < Be < B < C < N < O < F < Ne. The correct order is Li < B < Be < C < O < N < F < Ne.

• Isoelectronic size: Ignoring nuclear charge. Al³⁺ is the smallest and N³⁻ the largest in the series Al³⁺ < Mg²⁺ < Na⁺ < F⁻ < O²⁻ < N³⁻.

• Dipole moment of NH₃ and NF₃: Assuming NF₃ is more polar. In NH₃ the dipoles reinforce each other, while in NF₃ they oppose, so NH₃ has the larger dipole moment.

• Bond angles: Treating CH₄, NH₃ and H₂O as equal because all are sp³. More lone pairs mean a smaller angle (CH₄ > NH₃ > H₂O).

• Hydride trends: Confusing acidic strength with boiling point. Acidity rises as HF < HCl < HBr < HI, but HF has the highest boiling point because of hydrogen bonding.

• Electron removal in transition metals: Removing 3d electrons before 4s. For Fe²⁺, the configuration is [Ar] 3d⁶, not 3d⁴ 4s².

• Strong-field vs weak-field d⁶ complexes: Mixing up their magnetic nature. Strong-field (t₂g⁶ eg⁰) is diamagnetic, while weak-field (t₂g⁴ eg²) is paramagnetic with four unpaired electrons.

• Coordination number: Counting ligands instead of donor atoms. EDTA is one ligand but hexadentate, so it contributes six donor atoms.

• IUPAC naming: Using cyano or chloro instead of cyanido and chlorido, as in hexacyanidoferrate(III).

• Cu⁺ stability: Assuming Cu⁺ is stable in water. It disproportionates to Cu²⁺ and Cu because Cu²⁺ has a greater hydration enthalpy.

Inorganic Chemistry in NEET rewards students who combine NCERT facts with clear rules on periodic trends, bonding, coordination compounds and d- and f-block behaviour. Revise these PYQ patterns regularly, practise the exceptions, and you can turn this section into dependable marks on exam day.

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