NEET Chemistry — p-Block Elements Complete Chapter Guide

Chapter Overview & Weightage

p-Block Elements is the single highest-weightage chapter in NEET Chemistry. Covering Groups 13 to 18, it is vast — but NEET asks predictable patterns. Compound properties, structures, and reactions of specific elements dominate.

p-Block carries 8-10% weightage in NEET with 4-6 questions. This is the most important chapter in Inorganic Chemistry — and arguably in all of NEET Chemistry.

Year	NEET Q Count	Key Topics Tested
2025	5	Ozone, interhalogen, SO $_2$ structure
2024	4	Noble gas compounds, phosphorus allotropes
2023	5	Nitrogen oxides, halogens, Group 15
2022	6	Sulphuric acid, Group 14, interhalogen
2021	4	Boron compounds, Group 16, noble gases

graph TD
    A[p-Block Elements] --> B[Group 13: B, Al]
    A --> C[Group 14: C, Si]
    A --> D[Group 15: N, P]
    A --> E[Group 16: O, S]
    A --> F[Group 17: Halogens]
    A --> G[Group 18: Noble Gases]
    B --> H[Boron Hydrides, BF3]
    D --> I[Nitrogen Oxides, Phosphorus Allotropes]
    E --> J[Ozone, H2SO4 Manufacturing]
    F --> K[Interhalogen Compounds]
    G --> L[XeF2, XeF4, XeF6]

Key Concepts You Must Know

Tier 1 (Always asked)

Structures of ozone, SO $_2$ , SO $_3$ , H $_2$ SO $_4$
Interhalogen compounds (types: XY, XY $_3$ , XY $_5$ , XY $_7$ ) and their structures
Noble gas compounds: XeF $_2$ (linear), XeF $_4$ (square planar), XeF $_6$
Allotropes of phosphorus (white, red, black)
Oxides of nitrogen (N $_2$ O, NO, NO $_2$ , N $_2$ O $_3$ , N $_2$ O $_4$ , N $_2$ O $_5$ )

Tier 2 (Frequently asked)

Group trends: electronegativity, ionization energy, electron gain enthalpy
Anomalous behavior of first element in each group (B, C, N, O, F)
Boron compounds: borax, diborane structure (banana bonds)
Contact process (H $_2$ SO $_4$ ) and Ostwald process (HNO $_3$ )

Tier 3 (Occasional)

Silicones and silicates
Phosphazenes
Pseudo halides

Important Formulas

Ozone preparation: $3O_2 \xrightarrow{UV} 2O_3$

Contact process: $2SO_2 + O_2 \xrightleftharpoons{V_2O_5} 2SO_3$

Ostwald process: $4NH_3 + 5O_2 \xrightarrow{Pt} 4NO + 6H_2O$

Interhalogen formation: halogen with excess of less electronegative halogen gives higher type (XY $_3$ , XY $_5$ , XY $_7$ ).

Compound	Hybridization	Shape	Lone Pairs
XeF $_2$	sp $^3$ d	Linear	3 LP
XeF $_4$	sp $^3$ d $^2$	Square planar	2 LP
XeF $_6$	sp $^3$ d $^3$	Distorted octahedral	1 LP
XeO $_3$	sp $^3$	Pyramidal	1 LP
XeOF $_2$	sp $^3$ d	T-shaped	2 LP

For interhalogen compounds, the number of atoms bonded to the central halogen depends on size difference. Larger central atom + smaller surrounding atoms = higher coordination. IF $_7$ is the only interhalogen with coordination number 7 (iodine is large enough).

Solved Previous Year Questions

PYQ 1 — NEET 2024

Problem: Which of the following has a pyramidal structure? (a) XeO $_3$ (b) XeF $_4$ (c) XeF $_2$ (d) XeOF $_4$

Solution:

XeO $_3$ : Xe has 3 bond pairs + 1 lone pair = sp $^3$ hybridized. Shape is pyramidal (like NH $_3$ ).

XeF $_4$ : square planar. XeF $_2$ : linear. XeOF $_4$ : square pyramidal.

Answer: (a) XeO $_3$

PYQ 2 — NEET 2023

Problem: Which oxide of nitrogen is a mixed anhydride?

Solution:

N $_2$ O $_3$ is the mixed anhydride of HNO $_2$ and HNO $_3$ — wait, actually N $_2$ O $_3$ is the anhydride of HNO $_2$ alone.

N $_2$ O $_4$ is the dimer of NO $_2$ . N $_2$ O $_5$ is the anhydride of HNO $_3$ .

The mixed anhydride concept: N $_2$ O $_4$ can be considered a mixed anhydride since NO $_2$ + H $_2$ O gives both HNO $_2$ and HNO $_3$ .

Answer: N $_2$ O $_4$ (gives a mixture of HNO $_2$ and HNO $_3$ with water)

Students confuse anhydrides. The rule: if an oxide reacts with water to give a single acid, it is a simple anhydride. N $_2$ O $_5$ + H $_2$ O gives 2HNO $_3$ (simple). N $_2$ O $_4$ + H $_2$ O gives HNO $_2$ + HNO $_3$ (mixed).

Difficulty Distribution

Difficulty	% of Questions	What to Expect
Easy	30%	Structure identification, group trends
Medium	50%	Compound properties, reactions, processes
Hard	20%	Anomalous behavior, cross-group comparison

Expert Strategy

Week 1-2: Group 15, 16, 17 are the most tested. Focus on nitrogen oxides, sulphur compounds (SO $_2$ , SO $_3$ , H $_2$ SO $_4$ ), and halogens (interhalogen, oxoacids of halogens).

Week 3: Noble gas compounds and Group 13-14. XeF $_2$ , XeF $_4$ , XeF $_6$ structures appear almost every year. Boron compounds (borax bead test, diborane) are also regular.

Week 4: Revision with PYQs. p-Block has the most questions in the NEET PYQ bank. Sort by group and solve systematically.

Make a “structures” sheet listing the shape, hybridization, and bond angle of every important compound across Groups 13-18. This single sheet is worth 3-4 marks in NEET.

Common Traps

Trap 1 — Ozone is angular, not linear. O $_3$ has a bent structure (bond angle ~117 degrees) with sp $^2$ hybridization. The central oxygen has one lone pair. Students often draw it as linear by analogy with CO $_2$ .

Trap 2 — White phosphorus is P $_4$ (tetrahedral), not P. White phosphorus exists as discrete P $_4$ molecules with 60-degree bond angles (highly strained, hence reactive). Red phosphorus is polymeric and less reactive.

Trap 3 — HF is a weak acid despite fluorine being the most electronegative. The high bond dissociation energy of H-F (568 kJ/mol) makes it hard to dissociate in water. Acid strength among hydrohalic acids: HI > HBr > HCl > HF.

Trap 4 — Noble gases do form compounds. Xenon forms stable fluorides and oxides. The “noble gases are inert” rule has exceptions. Krypton also forms KrF $_2$ under extreme conditions.