Is P-Block Elements part of the EAPCET Chemistry syllabus?

Yes. P-Block Elements is taught in Intermediate second year Chemistry, and the EAPCET Engineering syllabus is based on the Intermediate first- and second-year syllabus. Check the official notification each year for any changes.

How many Chemistry questions are there in EAPCET?

40 of the 160 questions in the Engineering paper are Chemistry, spread across 24 chapters.

What mistakes do students make in P-Block Elements?

Taking basicity from the number of hydrogens in the formula — count only P–OH groups, so H₃PO₃ is dibasic, not tribasic. Saying F₂ has the highest bond enthalpy among halogens — Cl₂ does, because lone-pair repulsion weakens the short F–F bond. Calling HF the strongest hydrohalic acid because fluorine is most electronegative — HF is the weakest in water owing to its strong H–F bond; HI is strongest. Assigning XeF₄ a tetrahedral shape — xenon has two lone pairs (sp³d²), which makes it square planar.

EAPCET Chemistry · Intermediate second year

P-Block Elements

This chapter covers groups 15 to 18: nitrogen, oxygen, halogen and noble-gas families, their compounds and industrial processes.

Subject: Chemistry
Taught in: Intermediate second year
Chemistry in the paper: 40 of 160 questions

Key formulas and results

Ammonia is made by the Haber process and nitric acid by the Ostwald process
Sulphuric acid is made by the contact process
$\ce{H3PO3}$ is dibasic; $\ce{H3PO4}$ is tribasic
$\ce{XeF2}$ is linear, $\ce{XeF4}$ square planar and $\ce{XeF6}$ distorted octahedral
Fluorine is the most electronegative element and a powerful oxidising agent

What this chapter covers

Group 15: nitrogen family
Group 16: oxygen family
Group 17: halogens
Group 18: noble gases
Oxoacids
Industrial processes

How it is usually asked

Structures of oxoacids and xenon fluorides
Industrial processes
Trends within groups
Basicity of oxoacids

Understanding P-Block Elements

Groups 15 to 18 share a common story: the first element (N, O, F) is small, highly electronegative and has no d orbitals, so it behaves differently from the rest. Nitrogen forms a very strong N≡N triple bond and cannot exceed a covalency of four, which is why PCl₅ exists but NCl₅ does not. Down each group, metallic character increases, hydrides become less stable and more reducing, and the lower oxidation state becomes more stable through the inert pair effect.

Oxoacids are a frequent source of questions. Only hydrogens attached to oxygen (P–OH) are ionisable, so H₃PO₂ is monobasic, H₃PO₃ dibasic and H₃PO₄ tribasic; acids with P–H bonds act as reducing agents. Industrial processes appear often: ammonia by the Haber process (iron catalyst), nitric acid by the Ostwald process (platinum catalyst) and sulphuric acid by the contact process (V₂O₅ catalyst, with SO₃ absorbed in H₂SO₄ to form oleum).

Halogens are strong oxidising agents, with fluorine the strongest. Their bond enthalpy order is Cl₂ > Br₂ > F₂ > I₂, because lone-pair repulsion weakens F–F, and acid strength rises from HF to HI. Xenon forms fluorides whose shapes come from VSEPR: XeF₂ is linear (three lone pairs), XeF₄ square planar (two lone pairs) and XeF₆ distorted octahedral (one lone pair). EAPCET tests structures, basicity and trends within each group.

Worked example

EAPCET-style question

The basicity of hypophosphorous acid, $\ce{H3PO2}$ , is:

(1)0
(2)1
(3)2
(4)3

Solution

Basicity equals the number of ionisable hydrogens, which are the ones bonded to oxygen (P–OH).
Structure of $\ce{H3PO2}$ : phosphorus forms one P=O, one P–OH and two P–H bonds.
The two P–H hydrogens are not ionisable; only the one P–OH hydrogen is.
So $\ce{H3PO2}$ is monobasic, with basicity 1 — and its P–H bonds make it a good reducing agent.

Answer: 1

Shortcuts and results to remember

Solid $\ce{PCl5}$ is ionic, $\ce{[PCl4]+[PCl6]-}$ (tetrahedral sp³ cation and octahedral sp³d² anion), while gaseous $\ce{PCl5}$ is trigonal bipyramidal (sp³d).
Acid strength of the chlorine oxoacids rises with the oxidation number of chlorine: $\ce{HClO4} > \ce{HClO3} > \ce{HClO2} > \ce{HClO}$ .
Basicity of a phosphorus oxoacid equals the number of P–OH groups: H₃PO₂ is monobasic, H₃PO₃ and H₄P₂O₅ are dibasic, and H₃PO₄ is tribasic.

Common mistakes to avoid

Taking basicity from the number of hydrogens in the formula — count only P–OH groups, so H₃PO₃ is dibasic, not tribasic.
Saying F₂ has the highest bond enthalpy among halogens — Cl₂ does, because lone-pair repulsion weakens the short F–F bond.
Calling HF the strongest hydrohalic acid because fluorine is most electronegative — HF is the weakest in water owing to its strong H–F bond; HI is strongest.
Assigning XeF₄ a tetrahedral shape — xenon has two lone pairs (sp³d²), which makes it square planar.

How to prepare it

Most marks here come from structures — practise drawing oxoacids and xenon compounds.

Once the formulas feel familiar, test them the way the exam does: practise P-Block Elements questions chapter-wise, then attempt a full previous year paper to see whether it holds up under a 3-hour timer.

Related Chemistry chapters

See every chapter in the EAPCET Chemistry syllabus.

Practise P-Block Elements chapter-wise

Chapter-wise quizzes show exactly which topics in this chapter you still get wrong — before a full paper does.

Frequently asked questions

Is P-Block Elements part of the EAPCET Chemistry syllabus?: Yes. P-Block Elements is taught in Intermediate second year Chemistry, and the EAPCET Engineering syllabus is based on the Intermediate first- and second-year syllabus. Check the official notification each year for any changes.
How should I prepare P-Block Elements for EAPCET?: Most marks here come from structures — practise drawing oxoacids and xenon compounds.
How many Chemistry questions are there in EAPCET?: 40 of the 160 questions in the Engineering paper are Chemistry, spread across 24 chapters.
What mistakes do students make in P-Block Elements?: Taking basicity from the number of hydrogens in the formula — count only P–OH groups, so H₃PO₃ is dibasic, not tribasic. Saying F₂ has the highest bond enthalpy among halogens — Cl₂ does, because lone-pair repulsion weakens the short F–F bond. Calling HF the strongest hydrohalic acid because fluorine is most electronegative — HF is the weakest in water owing to its strong H–F bond; HI is strongest. Assigning XeF₄ a tetrahedral shape — xenon has two lone pairs (sp³d²), which makes it square planar.