CBSE Class 11 Chemistry Chapter 11: The p-Block Elements NCERT Solutions

Reviewed by NCERT Help Editorial Team · Updated on 29 Jul 2026

NCERT Solutions PDF Class 11 PDF

This resource provides detailed NCERT Solutions for Chapter 11, 'The p-Block Elements,' for CBSE Class 11 Chemistry. It focuses on Multiple Choice Questions (MCQs) that test understanding of the properties and behavior of p-block elements. The solutions explain concepts such as the physical states of elements, Lewis acidity, hybridization and geometry of complex species, the acidic nature of oxides, coordination numbers, and the acidic behavior of boric acid. Each solution is elaborated with step-by-step reasoning and relevant chemical principles, making it an excellent tool for students to grasp complex topics and prepare effectively for their examinations.

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Quick info

Board	CBSE
Class	Class 11
Subject	Chemistry Exemplar
Session	2026
Language	English
Type	NCERT Solutions
Chapter	Chapter 11

Chapter summary

Chapter 11, 'The p-Block Elements,' NCERT Solutions for Class 11 Chemistry covers key concepts related to Group 13 and 14 elements. This section focuses on MCQs, testing understanding of physical properties like melting points and liquid states, chemical properties such as Lewis acidity and the nature of oxides, and structural aspects like hybridization and coordination numbers. The solutions provide clear explanations for why certain elements exhibit specific behaviors, particularly highlighting the unique properties of boron and aluminum compounds, and the acidic nature of boric acid.

Learning outcomes

Understand the physical properties of p-block elements, including their state at different temperatures.
Identify and explain Lewis acids based on incomplete octets.
Determine the hybridization and geometry of complex species.
Analyze the acidic, basic, and amphoteric nature of oxides of p-block elements.
Explain the factors influencing coordination number and predict the possibility of complex formation.
Comprehend the acidic behavior of boric acid as a Lewis acid.

Topics covered

Paper topics

p-Block Elements
Group 13 Elements
Boron
Aluminum
Gallium
Indium
Physical Properties
Chemical Properties
Lewis Acids
Oxides of Elements
Hybridization
Coordination Number

Important topics

Lewis Acidity of Boron Compounds
Amphoteric Nature of Al₂O₃ and Ga₂O₃
Acidic Behavior of Boric Acid
Coordination Number Limitations
Hybridization and Geometry of Complex Ions

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Questions and Solutions

Multiple Choice Questions (MCQs) - Question 1

The element which exists in liquid state for a wide range of temperature and can be used for measuring high temperature is

Solution: The correct option is (c) Gallium (Ga). Gallium has a unique crystal structure that results in a low melting point (approximately 30°C) and a high boiling point. This wide liquid range, from around 30°C up to 2000°C, makes it exceptionally useful for applications requiring high-temperature measurements, such as in thermometers.

Multiple Choice Questions (MCQs) - Question 2

Which of the following is a Lewis acid?

AlCl3
(b) NaCl
(c) KCl
(d) MgCl2

Solution: The correct option is (a) AlCl3. A Lewis acid is a substance that can accept an electron pair. In aluminum chloride (AlCl3), the aluminum atom has only six valence electrons, meaning its octet is incomplete. To achieve a stable octet, it readily accepts an electron pair from a Lewis base, thus acting as a Lewis acid. Alkaline earth metals typically form ionic chlorides where the metal achieves a stable electron configuration.

Multiple Choice Questions (MCQs) - Question 3

The geometry of a complex species can be understood from the knowledge of the type of hybridisation of orbitals of the central atom. The hybridisation of the orbitals of the central atom in [B(OH)₄]⁻ and the geometry of the complex are respectively

sp³, tetrahedral
sp³, square planar
sp³d², octahedral
dsp², square planar

Solution: The correct option is (a) sp³, tetrahedral. In the complex ion [B(OH)₄]⁻, the central atom is Boron (B). Boron has 3 valence electrons. It forms four single bonds with the oxygen atoms of the four hydroxide (OH⁻) groups. This involves the formation of four sigma bonds. To accommodate these four bonds, the central boron atom undergoes sp³ hybridization. With four bond pairs and no lone pairs of electrons around the central atom, the geometry of the complex ion is tetrahedral.

Multiple Choice Questions (MCQs) - Question 4

Which of the following oxides is acidic in nature?

B₂O₃
Al₂O₃
Ga₂O₃
In₂O₃

Solution: The correct option is (a) B₂O₃. The acidic nature of oxides of elements in Group 13 generally decreases down the group, while basicity increases. Boron trioxide (B₂O₃) is a strongly acidic oxide. Aluminum oxide (Al₂O₃) and Gallium oxide (Ga₂O₃) are amphoteric, meaning they can react with both acids and bases. Indium oxide (In₂O₃) and Thallium oxide (Tl₂O₃) are predominantly basic in nature. The trend can be summarized as:

$\underbrace{\text{B}_2\text{O}_3}_{ \text{More acidic} }, \;\; \underbrace{\text{Al}_2\text{O}_3 \; \text{and} \;\; \text{Ga}_2\text{O}_3}_{ \text{Amphoteric} }, \;\; \underbrace{\text{In}_2\text{O}_3 \; \text{and} \; \text{Tl}_2\text{O}_3}_{ \text{Basic} }$

Multiple Choice Questions (MCQs) - Question 5

The exhibition of highest coordination number depends on the availability of vacant orbitals in the central atom. Which of the following elements is not likely to act as central atom in MF₆³⁻?

Solution: The correct option is (a) B. The formation of a complex ion like MF₆³⁻ requires the central atom (M) to have a coordination number of six. This typically involves the hybridization of orbitals to accommodate six bonding pairs. Boron (atomic number 5) has the electronic configuration 2, 3. It has vacant 2p orbitals but lacks vacant d-orbitals in its valence shell. Its maximum coordination number is generally limited to 4 (e.g., in [BF₄]⁻). Elements like Aluminum (Al), Gallium (Ga), and Indium (In) have vacant d-orbitals in their valence shells (or accessible d-orbitals in lower shells for Al) which can participate in hybridization (like sp³d²), allowing them to achieve a coordination number of six and form complexes such as [AlF₆]³⁻, [GaF₆]³⁻, and [InF₆]³⁻.

Multiple Choice Questions (MCQs) - Question 6

Boric acid is an acid because its molecule

contains replaceable H⁺ ion
gives up a proton
accepts OH⁻ from water releasing proton
combines with proton from water molecule

Solution: The correct option is (c) accepts OH⁻ from water releasing proton. Boric acid (H₃BO₃ or B(OH)₃) is a weak monoprotic acid. It does not donate a proton directly. Instead, it acts as a Lewis acid by accepting a hydroxide ion (OH⁻) from a water molecule. This process leaves a proton (H⁺) in the solution, making it acidic. The reaction can be represented as:

$H_3BO_3 + H_2O \longrightarrow B(OH)_4^- + H^+$

Alternatively, it can be written as:

$B(OH)_3 + 2H_2O \longrightarrow [B(OH)_4]^- + H_3O^+$

The boron atom in B(OH)₃ has an incomplete octet, which drives its ability to accept the electron pair from the hydroxide ion.

Common mistakes

Confusing Lewis acids with Brønsted-Lowry acids.
Incorrectly determining the hybridization or geometry of complex ions.
Misinterpreting the trend in acidic/basic nature of oxides down a group.
Not considering the availability of vacant orbitals when predicting coordination numbers.

Revision tips

Focus on understanding the 'why' behind each property, not just memorizing facts.
Draw structures and electron configurations to visualize hybridization and bonding.
Compare and contrast the properties of elements within the same group.
Practice identifying Lewis acids and bases in different chemical contexts.
Review the reactions of boric acid to understand its acidic nature.

Practice MCQs

Q1. Which element among Boron (B), Aluminum (Al), Gallium (Ga), and Indium (In) exists in a liquid state over a wide temperature range and is suitable for measuring high temperatures?

Q2. Identify the Lewis acid among the following options.

Q3. What is the hybridization of the central atom in the complex ion [B(OH)4]⁻, and what is its resulting geometry?

Q4. Which of the following oxides of Group 13 elements is acidic in nature?

Q5. Which element from Group 13 is unlikely to form a complex ion of the type MF₆³⁻ due to limitations in coordination number?

Q6. Boric acid (H₃BO₃) is considered an acid because it:

Frequently asked questions

What is the main focus of these NCERT Solutions for Class 11 Chemistry Chapter 11?

These solutions focus on providing detailed explanations for the Multiple Choice Questions (MCQs) presented in the NCERT Exemplar for Chapter 11, 'The p-Block Elements,' covering key concepts and properties of these elements.

Why is Gallium (Ga) used in high-temperature thermometers?

Gallium has a low melting point (around 30°C) and a high boiling point, allowing it to remain liquid over a wide temperature range, making it suitable for measuring high temperatures.

How does Boric acid act as an acid?

Boric acid acts as a Lewis acid by accepting a hydroxide ion (OH⁻) from water, which then releases a proton (H⁺) into the solution, thus increasing the acidity.

What determines the coordination number of an element?

The coordination number depends on factors like the availability of vacant orbitals in the central atom and steric considerations. For example, Boron's limited vacant orbitals restrict its coordination number.

Are the oxides of Group 13 elements consistently acidic?

No, the nature of oxides changes down the group. B₂O₃ is acidic, Al₂O₃ and Ga₂O₃ are amphoteric, and In₂O₃ and Tl₂O₃ are basic.

How can I use these solutions for exam revision?

These solutions help by clarifying the reasoning behind each answer. Review the explanations to understand the underlying chemical principles, which is crucial for tackling similar questions in exams.

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