Important Questions for CBSE Class 11 Chemistry Chapter 9 – Hydrogen

Class 11 Chemistry Chapter 9 Important Questions – Hydrogen

The utilisation of Hydrogen as an energy source can significantly reduce the world’s concern over energy. Hydrogen has significant industrial value in many ways. Therefore, you must expand your knowledge base in this arena. Chapter 9 of Class 11 Chemistry is about Hydrogen. The chapter puts the first step on how knowledge of hydrogen’s structure and application might help develop valuable compounds and new technologies in the future.

Students studying Chemistry should begin by reading the NCERT textbook for Class 11 Chemistry. Because Chemistry is a practical subject, students can deepen their grasp by working through various problems from the NCERT textbooks. 

Students can rely on Extramarks online learning platform as it provides the most authentic, comprehensive and reliable study solutions from Class 1 to Class 12. Extramarks website has a variety of NCERT-based study solutions including NCERT solutions, CBSE revision notes, CBSE past years’ question papers, and an NCERT-based important set of questions and answers.

Students are recommended to regularly practise questions from Extramarks curated question bank of Class 11 Chemistry Chapter 9 Important Questions. Our expert Science faculty members give students a list of important questions from the CBSE curriculum. To create a list of questions, the Extramarks team refers to NCERT Books, other significant reference materials, CBSE sample papers, CBSE past years’ question papers, etc. The students might feel more prepared for their exams by working through several questions from our Important Questions Class 11 Chemistry Chapter 9.

Students can register at Extramarks to access Chemistry Class 11 Chapter 9 Important Questions, NCERT solutions, revision notes, and other study materials, which will help them prepare for exams to the best of their ability.

Get Access to CBSE Class 11 Chemistry Important Questions 2022-23 with Solutions

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CBSE Class 11 Chemistry Important Questions
Sr No Chapters Chapter Name
1 Chapter 1 Some Basic Concepts of Chemistry
2 Chapter 2 Structure of Atom
3 Chapter 3 Classification of Elements and Periodicity in Properties
4 Chapter 4 Chemical Bonding and Molecular Structure
5 Chapter 5 States of Matter
6 Chapter 6 Thermodynamics
7 Chapter 7 Equilibrium
8 Chapter 8 Redox Reactions
9 Chapter 9 Hydrogen
10 Chapter 10 The s-Block Elements
11 Chapter 11 The p block Elements
12 Chapter 12 Organic Chemistry – Some Basic Principles and Techniques
13 Chapter 13 Hydrocarbons
14 Chapter 14 Environmental Chemistry

Hydrogen Class 11 Important Questions and Answers

Extramarks has prepared Important Questions Class 11 Chemistry Chapter 9 to help students get a consolidated question bank from different sources. By solving these questions students will be able to revise the concepts covered in the Hydrogen chapter and other related terms properly by utilising this material.

Below is a list of a few questions and their solutions from our question bank of Important Questions Class 11 Chemistry Chapter 9.

Question 1. What are metallic/interstitial hydrides? How do they differ from molecular hydrides?

Answer 1:

A hydride is a binary chemical made up of an element and an atom of Hydrogen.

Metallic hydrides are also known as interstitial hydrides. Compounds called metallic/interstitial hydrides are formed when transition metals and Hydrogen are bound together. They are the source of many d-Block and f-Block components. These hydrides are conductors of both heat and electricity.

Molecular hydrides are hydrides that contain additional electronegative atoms bonded to the H-atom. Molecular hydrides have a low electrical conductivity compared to metallic hydrides. While molecular hydrides exist in a gaseous state, metallic hydrides only exist in a solid state.

Interstitial or metallic hydrides are created when hydrogen bonds with transition metals; molecular hydrides, on the other hand, also contain hydrogen bonds with an electronegative atom.

Question 2: Why does Hydrogen occur in a diatomic form rather than a monoatomic form under normal conditions?

Answer: 2 The hydrogen atom has a higher ionisation enthalpy. As a result, taking its electron out is more difficult. It thus tends to exist in low monoatomic form. Instead, Hydrogen forms a covalent bond with another hydrogen atom to form a diatomic molecule.

Question 3: If the same mass of liquid water and a piece of ice is taken, then why is the density of ice less than that of liquid water?

Answer 3:

Mass per unit volume, or mass/volume, is the unit used to measure density. Water expands as it freezes; therefore, there is more ice than liquid water for a given amount of water. In other words, ice floats on water because it has a lower density than liquid water.

Question 4: What do you understand by the term “non-stoichiometric hydrides”? Do you expect this type of hydride to be formed by alkali metals? Justify your answer.

Answer 4: Hydrogen-deficient compounds are known as non-Stoichiometric hydrides. These are created when dihydrogen reacts with d-block and f-block elements. They do not adhere to the law of constant composition in these hydrides.

E.g.:  LaH2.87, YbH2.55, TiH 1.5 – 1.8

Alkali metals form stoichiometric hydrides that are naturally ionic. Alkali metal ions and hydride ions are of similar size (208 pm). The hydride ion and the constituent metal experience a significant binding force, forming Stoichiometric hydrides.

Question 5: Complete the following equations:

(i) PbS(s)    +  H2O2(aq) → 

(ii) CO(g)  + 2H2(g) CobaltCatalyst  ?

Answer 5:

(i) PbS + 4H2O2 → PbSO4 + 4H2O [Redox reaction]

(ii) CO + 2H2 → CH3OH [Redox reaction]

Question 6: How do you expect the metallic hydrides to be useful for hydrogen storage? Explain

Answer 6: Metallic hydrides are deficient in Hydrogen. The law of constant composition does not apply to them.

It has been determined that Hydrogen occupies the interstitial position in the lattices of the hydrides of Pd, Ac, Ni, and Ce, allowing for further hydrogen absorption on these metals.

A significant amount of Hydrogen can be stored in metals like Pt and Pd. Thus, metallic hydrides are employed to store Hydrogen and as an energy source.

Question 7: Give reasons:

(i) Lakes freeze from the top towards the bottom.

(ii) Ice floats on water.

Answer 7:

(i) Due to low temperatures in winter, the lake freezes from top to bottom. Because the cold water is heavier than the warm water, it sinks to the bottom. As it reaches the surface, warm water replaces it. The cycle repeats until the mercury falls below 4 degrees when the lake freezes completely.

(ii)  Due to the structure of the ice, it leaves empty spaces between water molecules (i.e. four hydrogen atoms surround one oxygen atom). Thus,  ice can float on the water since its density is lower than water.

Question 8: How does the atomic Hydrogen or oxy-hydrogen torch function for cutting and welding purposes? Explain.

Answer 8: Another name for the atomic hydrogen torch is the oxy-hydrogen torch. With the aid of an electric arc, which releases a significant amount of energy, these atoms are created through the dissociation of dihydrogen. The total energy released is 435.88 kJ mol-1. This energy is used to create a temperature of 4000 K, which is necessary for metal cutting and welding. In order to generate a specific temperature on the particular surface that needs to be welded, atomic hydrogen torches are utilised for this purpose.

Question 9: What do you understand by the term ‘auto protolysis of water? What is its significance?

Answer 9:

Two water molecules are converted into hydronium ions and hydroxide ions are known as the autoprotolysis of water. This type of self-ionisation occurs in water.

2H2O → H3O+    +       OH

The reaction shows the amphoteric characteristic of water. It can act as a base as well as an acid. Electrons are supplied by one water molecule and absorbed by the other.

Question 10: Describe the structure of the common form of ice.

Answer 10: Ice is typically water in its crystalline state. If it crystallises at atmospheric pressure, it takes on a visible hexagonal shape. It condenses to a cubic shape at very low temperatures.

The Structure of Ice

In the 3 – D ice structure, hydrogen bonds and a highly organised structure are present. At a distance of 276 pm, four oxygen atoms form a tetrahedron around each individual oxygen atom. Ice’s structure also includes large gaps that can accommodate specific-sized molecules.

Question 11: Discuss briefly the de-mineralisation of water by ion exchange resin.

Answer 11:

De-mineralisation of water is the process of removing all soluble salts from it through cation and anion exchange. In the cation exchange process, sodium, calcium, and magnesium cations change places with hydrogen cations. During the anion exchange procedure, OH is exchanged. These two elements work together to produce water.

H+      +        OH →    H2O

Question 12: What causes the temporary and permanent hardness of water?

Answer 12: Hardness in water persists because it contains soluble magnesium and calcium salts in the form of chlorides.

Hardness in water is only temporary since it contains soluble calcium and magnesium salts in the form of hydrogen carbonates.

Question 13: Molecular hydrides are classified as electron deficient, electron precise and electron-rich compounds. Explain each type with two examples.

Answer 13:

Electron deficient: A compound is said to be electron-deficient if it lacks enough electrons for the central atom’s octet to be completed. These compounds lack the necessary electrons to form the common electron-pair bonds between each pair of connected atoms.

Examples: Compounds like  B2F6 and Al2Cl6 have less than 8 electrons in their valence shells. 

Electron precise: Electron-precise hydrogen compounds have enough valence electrons to form covalent bonds. Those hydrides that possess the precise number of electrons required to form a covalent bond are said to be electron-precise hydrides. These compounds are frequently made with group 14 components. The compounds often take the shape of tetrahedra.

Examples: CH4 and SiH4

Electron rich: Hydrides that contain more electrons than are necessary for bonding are said to be electron-rich hydrides. Most of the additional electrons come from the lone pair of electrons on the core atom. The majority of the components in these compounds come from groups 15, 16, and 17.

Examples: NH3  and  PH3

Question 14: Is demineralised or distilled water useful for drinking purposes? If not, how can it be made useful?

Answer 14: We cannot survive without water. It contains a large number of dissolved nutrients that are essential to both people and plants and animals. Demineralised water cannot be used for drinking since it is devoid of any soluble minerals.

This water can be used when the desired minerals are added in the precise amounts needed for growth.

Question 15: Write one chemical reaction for the preparation of D2O2.

Answer 15:

D2O2 can be prepared when D2SO4 is dissolved in water and then reacts with BaO2.

The chemical reaction is as follows:  BaO2 + D2SO4 → BaSO4 + D2O

Question 16: Describe the usefulness of water in the biosphere and biological systems.

Answer 16: The usefulness of water in the biosphere and biological systems are as follows:

  • Water is essential for all life forms, including plants and humans, which together make up about 65% of the human body. It is essential to the biosphere because of its  Thermal conductivity,  Dipole moment,  Specific heat,  Dielectric constant and surface tension.
  • For regulating the atmospheric climate and the body temperatures of all living things, the heat capacity and the heat of vapourisation are quite helpful.
  • It serves as a carrier of many nutrients that both plants and animals need for a variety of metabolic processes.

Question 17: (i) Draw the gas phase and solid phase structure of H₂O₂.

(ii) H₂O₂ is a better oxidising agent than water. Explain.

Answer 17:

(i) The structure of gas and solid phases of H2O2 have slight variations.

Gas Phase and Solid Phase

(ii) H2O2 is a more effective oxidising agent than water because it changes an acidified KI solution into I2, which gives the starch solution a blue colour but not water. In addition, H2O2 is the only substance that can turn black PbS into white PbSO4, not water.

Question 18: Knowing the properties of H2O and D2O, do you think that D2O can be used for drinking purposes?

Answer 18: D2O is referred to as “heavy water” and serves as a moderator (slows down the rate of reaction). This characteristic prevents it from being used for drinking because it slows down catabolic and anabolic reactions. These changes in the body may cause a casualty.

Question 19: Dihydrogen reacts with dioxygen (O₂) to form water. Write the name and formula of the product when the isotope of Hydrogen, which has one proton and one neutron in its nucleus, is treated with oxygen. Will the reactivity of both the isotopes be the same towards oxygen? Justify your answer.

Answer 19:

One proton and one neutron make up the hydrogen isotope deuterium (D). Dideuterium interacts with dioxygen to produce deuterium oxide, sometimes known as heavy water.

With oxygen, H2 and D2 will react in very different ways. H2 is more reactive than D2 in oxygen reactions because the D-D bond is stronger than the H-H bond.

Question 20: What is the difference between the terms ‘hydrolysis’ and ‘hydration’?

Answer 20: The difference between the terms ‘hydrolysis’ and ‘hydration’ is as follows:

Hydration: It is the process by which one or more molecules are added to a molecule or an ion to produce hydrated compounds.

CuSO4   +  5H2O    →  CuSO4.5H2O

Hydrolysis: It is the name for a chemical reaction in which a substance reacts with hydroxide ions and Hydrogen from water molecules to produce products.

NaH  + H2O   →  NaOH  + H2

Question 21: Explain why HCI is a gas and HF is a liquid.

Answer 21:

Intermolecular hydrogen bonds join HF molecules. As a result, HF is a liquid at room temperature. Since the HCl molecules lack intermolecular hydrogen bonds, it is a gas at room temperature.

Question 22: How can saline hydrides remove traces of water from organic compounds?

Answer 22: Saline hydrides are ionic by nature. Water and saline hydrides react, releasing hydrogen gas and forming metal hydroxide in the process. When introduced to an organic solvent, they cause the water to react. 

AH(S)  +  H2O(l)  →  AOH(aq)   +   H2(g)

The metallic hydroxide is left behind as the Hydrogen escapes into the environment. The dry organic solvent separates over.

Question 23: When the first element of the periodic table is treated with dioxygen, it gives a compound whose solid-state floats on its liquid state. This compound has the ability to act as an acid as well as a base. What products will be formed when this compound undergoes autoionisation?

Answer 23:

The first element in the periodic table is H, and its molecule is dihydrogen (H2). Dihydrogen reacts with dioxygen to form water. Water is fluid when it’s at a normal temperature. As water freezes, it expands to form ice. In other words, ice floats on top of liquid water because it is less dense than water.

In its natural state, water is amphoteric, acting as a base in the presence of strong acids and acids when strong bases are present.


It happens that conjugate bases and acids are formed. This process of water self-ionisation is known as auto-protolysis.

Question 24: How does H2 O2 behave as a bleaching agent?

Answer 24: In both basic and acidic conditions, hydrogen peroxide functions as an effective oxidising agent. When introduced to the fabric, it breaks down the chromophores’ (colour-producing agents) chemical bonds. As a result, the cloth becomes whiter, and the visible light is not absorbed.

Question 25: Hydrogen generally forms covalent compounds. Give a reason.

Answer 25:

Hydrogen tends to form covalent compounds because it shares its electron with other elements. Hydrogen is an element with an atomic number of one and only one electron. Since it cannot lose an electron, it prefers to share electrons with other atoms, forming covalent compounds.

Question 26: Why is water an excellent solvent for ionic or polar substances?

Answer 26: Water functions as a polar solvent due to its high dielectric constant. The high dielectric constant of water reduces the attraction between cation and anion.  Therefore, water molecules can easily remove ions from the lattice site using dipole forces.

Question 27: Why is the Ionisation enthalpy of Hydrogen higher than that of sodium?

Answer 27:

The H atom has a higher nuclear attraction than the Na atom; hence it takes more energy to remove a valence electron from it. Because of this, Hydrogen’s ionisation enthalpy (1312 kJ/mol) is higher than sodium’s (496 kL/mol).

Question 28: Which fuel is used as rocket fuel?

Answer 28: Since Hydrogen is both light and incredibly strong, it is employed as rocket fuel. It burns extremely hot and has the smallest molecular weight of any known chemical.

Question 29: What is the importance of heavy water?

Answer 29:

In nuclear reactors, heavy water is used as a neutron moderator to slow down neutrons and increase the likelihood that they will interact with fissile uranium-235 rather than the neutron-collecting uranium-238.

In studying reaction mechanisms and manufacturing other deuterium compounds like CD4, D2SO4, and others, it is used as a tracer chemical.

Question 30: What is the behavioural similarity between NH3, H2O, and HF compounds?

Answer 30: They act as electron donors or Lewis bases. Lone pairs on highly electronegative atoms like N, O, or F in hydrides cause hydrogen bonds between molecules.

Question 31: With the help of suitable examples, explain the property of H₂O₂ that is responsible for its bleaching action.

Answer 31:

The unstable oxygen that H2O2 produces after its breakdown causes it to bleach materials.  

      H2O2 → H2O + [O] 

A coloured substance that has been exposed to nascent oxygen becomes colourless. Feathers, silk, wool, ivory, and other materials can all be bleached using this method. It can be used to bleach paper, oils, and fats.

Question 32: What is the pH of water?

Answer 32: pH determines the concentration of hydrogen ions (H+) in a solution. In pure water, random processes that produce the ions H+ and OH tend to produce ions. The amount of H+ generated in pure water is roughly similar to an OH. Because of this, a pH of 7 is regarded as neutral.

Question 33: Why is hydrogen peroxide stored in wax-lined bottles?

Answer 33:

The rough surfaces of glass break down hydrogen peroxide, any alkali oxides present and light. H2O2 is often stored in coloured Teflon or plastic bottles covered with paraffin wax to avoid decomposition.

Question 34: Why is dihydrogen gas not preferred in balloons?

Answer 34: Dihydrogen should have been used in balloons because it is the lightest gas. However, it is not advised due to its combustibility.

Question 35: How will you account for the 104.5° bond angle in water?

Answer 35:

Two lone pairs of electrons exist after two of an oxygen atom’s six electrons are linked to a hydrogen atom. These lone pairs of electrons provide the bond angle in H2O with a value of 104.5°. This can be explained by the valence shell electron pair repulsion concept (VSEPR).

The sp3 hybridisation of the oxygen in the H2O molecule produces the tetrahedral structure. Lone pairs occupy two spots, and H atoms occupy two positions by forming sigma bonds with two hybrid orbitals. The actual bond angle is 104.5°, as opposed to the expected bond angle of 109.5°. In comparison to bond pairs, lone pairs are more repellent to one another. The result is a decrease in the bending angle of water from 109.5° to 104.5°.

Question 36: Atomic hydrogen combines with almost all elements but molecular Hydrogen does not. Explain.

Answer 36:

Atoms of Hydrogen are incredibly brittle. Atomic Hydrogen needs one more electron to complete its electronic configuration and attain stability because it is in the 1s1 state. Atomic Hydrogen is particularly reactive as a result, reacting with almost every element. However, it interacts in three different ways: first, by losing one electron to H+, second, by gaining one electron from H+, and third, by creating single covalent bonds by exchanging electrons with other atoms. 

On the other hand, the H-H bond has a very high bond dissociation energy (435.88 kJ/mol1). As a result, only a few elements can react with molecular Hydrogen at room temperature.

Benefits of solving Important Questions of Hydrogen Class 11 Chemistry Chapter 9

Science depends heavily on Chemistry, which is frequently linked to other fields of study. With a good amount of success, Chemistry has recently assisted in addressing some of the urgent issues of environmental deterioration. One needs to fully understand the fundamentals of Chemistry in Class 11 and Class 12 which start with regular chapter revisions and answering a lot of exam-oriented questions.

Students can develop a solid foundation in the topic by going through Extramarks Important Questions Class 11 Chemistry Chapter 9. This will help them significantly when they are solving practical numerical problems during their exams.

Here are a few benefits students can achieve while solving the Important Questions Class 11 Chemistry Chapter 9

  • All the class 11 chemistry chapter 9 important questions exam questions are available in one place. The questions would’ve been taken from NCERT textbooks, previous exam questions, and other reference books, giving the chapter a complete study.
  • The questions from the entire chapter are covered in the Important Questions Class 11 Chemistry Chapter 9 list, ensuring that answering them aids in preparing the chapter as a whole.
  • The solutions are created by a team of subject matter experts from Extramarks who have years of experience teaching students in Chemistry and other science subjects. Students can, therefore, entirely rely on the solutions. Our team has provided detailed solutions that assist students in learning important concepts that are utilised in answering problems.

Extramarks provides top-notch resources for students of all Classes from 1-12, including NCERT review notes, CBSE sample papers, CBSE past years’ question papers, CBSE extra questions, and CBSE mock exams. Some of these resources can be accessed by students by visiting the sites listed below:

Q.1 Give the industrial method of preparation of H2O2



Industrially, H2O2 is prepared by the auto-oxidation of 2-ethylanthraquinol. The process involves a cycle of reactions. The net reaction is the catalytic union of H2 and O2 to give H2O2.

Q.2 Identify X and Y in the following reaction.


(a) X NaD, Y DO
(b) X Na2O, Y D2
(c) X Na2D, Y DO
(d) X NaOD, Y D2




Q.3 Which one is used as a moderator in nuclear reactors
A. Heavy water
B. Hard water
C. Mineral water
D. Unionized water



A. Heavy water

Explanation: Heavy water (D2O) is used as a moderator in nuclear reactors.

Q.4 Nascent hydrogen consists of
A. solvated protons
B. hydrogen ions in the excited state
C. hydrogen molecules with excess energy
D. hydrogen atoms with excess energy



C. hydrogen molecules with excess energy

Explanation: Nascent hydrogen is formed by the dissociation of molecular hydrogen. It contains excess energy.

Q.5 Choose the correct answer out of the following choices.
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

Assertion: D2O is called heavy water.
Reason: Degree of dissociation of D2O is high.



D2O is called heavy water and due to stronger D-O bonds, the degree of dissociation of D2O is lower than that of H2O.

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FAQs (Frequently Asked Questions)

1. Where can students easily find Important Questions Class 11 Chemistry Chapter 9?

A list of important questions in Class 11 Chemistry Chapter 9 is provided by Extramarks to help students learn, review, and be ready for their exams. Topics from every little corner of the chapters are covered with this extensive set of questions compiled by experts, ensuring that students receive good exam results. You can relax knowing that the answers to the Important Questions Class 11 Chemistry Chapter 9  are accurate and credible.

2. Is the hydrogen chapter important for NEET?

NEET is one of the most competitive exams in the country and is almost conducted every year for admission to undergraduate medical courses. The hydrogen chapter holds a 3-4% weightage in the examination. Though the weightage is low, students should not neglect it. This is because every single mark is crucial for such a competitive examination and can play in a pivotal role in your selection process.

3. What are the important topics covered in Class 11 Chemistry Chapter 9?

Every topic in Class 11 chemistry is crucial to building a solid foundation for Class 12 and subsequent higher education. Chapter 9 Class 11 Chemistry Important Questions covers a variety of topics, including

  • The position of Hydrogen in the periodic table.
  • Isotopes of Hydrogen.
  • Dihydrogen.
  • Hydrides.
  • Water.
  • Hydrogen Peroxide.
  • Dihydrogen as a fuel.