Last Updated: April 2026
The p-Block Elements chapter is one of the most formula-intensive topics in JEE Main Chemistry, contributing 2-4 questions every year. This chapter covers Groups 13-18 across two NCERT chapters (Class 11 Chapter 11 and Class 12 Chapter 7). A systematic approach to this chapter — covering oxidation states, allotropes, key reactions, and anomalous behaviour — can secure 8-16 marks in JEE Main 2027.
p-Block — JEE Main Weightage
| Groups | NCERT Chapter | JEE Main Questions (Avg) | Key Topics |
|---|---|---|---|
| Group 13-14 (Boron, Carbon families) | Class 11, Ch 11 | 1-2 | Boron anomaly, allotropes of carbon, silicates |
| Group 15-18 (N, O, Halogens, Noble gases) | Class 12, Ch 7 | 1-2 | Oxoacids, interhalogen compounds, ozone |
| Total | — | 2-4 | — |
Group 13 — Boron Family
Key Points
- Boron is a metalloid; rest are metals
- Boron is an electron-deficient element (only 3 valence electrons)
- Boron anomaly: Unlike Al, Ga, In, Tl — boron doesn’t form B³⁺ ions (small size, high ionisation energy)
- Boron forms covalent compounds exclusively
Important Boron Compounds
| Compound | Formula | Structure | JEE Importance |
|---|---|---|---|
| Borax | Na₂B₄O₇·10H₂O | Contains [B₄O₅(OH)₄]²⁻ unit | Very High (borax bead test) |
| Diborane | B₂H₆ | 3-centre 2-electron bonds (banana bonds) | Very High |
| Boron trifluoride | BF₃ | Trigonal planar, Lewis acid | High |
| Borazine | B₃N₃H₆ | “Inorganic benzene” | Medium |
Group 14 — Carbon Family
Allotropes of Carbon
| Allotrope | Structure | Hybridisation | Property |
|---|---|---|---|
| Diamond | 3D tetrahedral network | sp³ | Hardest natural substance, non-conductor |
| Graphite | Layered hexagonal sheets | sp² | Conductor (delocalised π electrons), lubricant |
| Fullerene (C₆₀) | Spherical cage, 60 carbons | sp² | 20 hexagons + 12 pentagons; superconductor when doped |
| Graphene | Single layer of graphite | sp² | Strongest known material, excellent conductor |
Important Compounds — Group 14
- CO: Strong reducing agent; poisonous (binds haemoglobin 200× stronger than O₂)
- CO₂: Acidic oxide; linear molecule; greenhouse gas
- Silicones: Polymers with Si-O-Si backbone; water repellent
- Silicates: Basic unit = SiO₄⁴⁻ tetrahedral; shared oxygen links them into chains, rings, sheets, 3D networks
Group 15 — Nitrogen Family
Oxoacids of Nitrogen — Must Know
| Acid | Formula | Oxidation State of N | Nature |
|---|---|---|---|
| Hyponitrous acid | H₂N₂O₂ | +1 | Weak acid |
| Nitrous acid | HNO₂ | +3 | Weak, unstable |
| Nitric acid | HNO₃ | +5 | Strong, oxidising |
Ammonia (NH₃)
- Prepared by Haber’s process: N₂ + 3H₂ ⇌ 2NH₃ (Fe catalyst, 200 atm, 500°C)
- Pyramidal shape (sp³, 1 lone pair); acts as Lewis base (electron pair donor)
Nitric Acid (HNO₃)
- Prepared by Ostwald’s process: 4NH₃ + 5O₂ → 4NO + 6H₂O (Pt/Rh catalyst, 500°C)
- Dilute HNO₃ with metals: 8HNO₃(dilute) + 3Cu → 3Cu(NO₃)₂ + 2NO↑ + 4H₂O
- Conc HNO₃ with metals: 4HNO₃(conc) + Cu → Cu(NO₃)₂ + 2NO₂↑ + 2H₂O
- Aqua regia: 3HCl + HNO₃ — dissolves gold and platinum
- Passivation: Conc HNO₃ renders Fe, Al passive (thin oxide layer)
Group 16 — Oxygen Family
Ozone (O₃)
- Angular structure; sp² hybridised oxygen
- Strong oxidising agent: O₃ → O₂ + [O] (nascent oxygen)
- Ozone layer absorbs UV radiation (220-330 nm) in stratosphere
- Depletion by CFCs: Cl• + O₃ → ClO + O₂ (chain reaction)
Sulphuric Acid (H₂SO₄)
- Prepared by Contact process: 2SO₂ + O₂ ⇌ 2SO₃ (V₂O₅ catalyst, 450°C); SO₃ + H₂SO₄ → H₂S₂O₇ (oleum); H₂S₂O₇ + H₂O → 2H₂SO₄
- Hot conc H₂SO₄: strong oxidising agent (oxidises metals, non-metals)
- Dilute H₂SO₄: not oxidising; reacts as acid
Group 17 — Halogens
Interhalogen Compounds
| Type | Example | Shape |
|---|---|---|
| XX’ (1:1) | ClF, BrF, BrCl | Linear |
| XX’₃ (1:3) | ClF₃, BrF₃ | T-shape |
| XX’₅ (1:5) | ClF₅, BrF₅ | Square pyramidal |
| XX’₇ (1:7) | IF₇ | Pentagonal bipyramidal |
Practice MCQs — JEE Chemistry p-Block 2027
Q1. The structure of diborane (B₂H₆) contains:
(A) 2-centre 2-electron bonds only (B) 3-centre 2-electron banana bonds (C) 3-centre 4-electron bonds (D) Ionic bonds
Answer: (B) B₂H₆ has two 3-centre 2-electron (banana) B-H-B bonds bridging the two boron atoms
Q2. Which is the correct order of acidic strength of oxoacids of Cl?
(A) HOCl > HClO₂ > HClO₃ > HClO₄ (B) HClO₄ > HClO₃ > HClO₂ > HOCl (C) HOCl > HClO₄ > HClO₃ > HClO₂ (D) HClO₃ > HClO₄ > HClO₂ > HOCl
Answer: (B) Acidic strength increases with oxidation state of Cl (more non-bonding O atoms = stronger acid)
Q3. In the Contact Process for manufacturing H₂SO₄, the catalyst used is:
(A) Iron (B) Platinum (C) V₂O₅ (D) MnO₂
Answer: (C)
Q4. The hybridisation of nitrogen in N₂O₅ is:
(A) sp (B) sp² (C) sp³ (D) sp³d
Answer: (B) N₂O₅ = NO₂⁺NO₃⁻; the NO₂⁺ nitrogen is sp hybridised and NO₃⁻ nitrogen is sp² hybridised. Overall in the molecular form, both N are sp²
Q5. Which of the following is NOT a property of noble gases?
(A) High ionisation energy (B) Non-zero electron affinity in all cases (C) Monoatomic in gaseous state (D) Chemically inert under normal conditions
Answer: (B) Noble gases have very low (essentially zero) electron affinity since their outer shell is complete
Frequently Asked Questions
How many questions from p-Block Elements appear in JEE Main?
JEE Main typically has 2-4 questions from p-Block Elements combined (Groups 13-18). In recent years, questions have focused on diborane structure, oxoacids, interhalogen compounds, allotropes of carbon, and industrial processes (Contact Process, Haber’s Process). In JEE Advanced, p-Block questions are more mechanistic and conceptual.
What are the most important reactions from p-Block for JEE 2027?
The most important reactions for JEE 2027 p-Block include: (1) Disproportionation reactions of halogens with NaOH (hot vs cold); (2) Reaction of non-metals with concentrated H₂SO₄ and HNO₃; (3) Preparation of HNO₃ by Ostwald’s process; (4) Preparation of H₂SO₄ by Contact process; (5) Diborane formation and hydroboration; (6) Reactions of noble gas compounds of xenon (XeF₂, XeF₄, XeF₆).
Also study: JEE Electrochemistry 2027 | JEE Thermodynamics | Free JEE Mock Test