Class 9 Chemistry – Exercise Short Questions & CRQs with Easy Answers
Based on ALP 2025–26
📘 Chapter 1: States of Matter and Phase Changes
Q1 (i): Why is there a need to divide Chemistry into many branches? Give three reasons.
Ans: Chemistry is a vast subject. It is divided into branches to:
1. Study specific aspects in detail.
2. Focus on different types of substances and their reactions.
3. Help scientists achieve breakthroughs in their own fields.
Q2 (ii): Reactions may take place due to electrons outside the nucleus or inside the nucleus. Which branches cover these two types?
Ans: Reactions due to electrons outside nucleus are studied in organic, inorganic, and physical chemistry. Reactions inside nucleus are studied in nuclear chemistry.
Q3 (v): Why are supercritical fluids important?
Ans: Supercritical fluids show properties of both gases and liquids. They can carry out chemical reactions that are not possible in ordinary solvents. Example: supercritical CO₂.
Q4 (vi): In which state does matter exist in the Sun?
Ans: Plasma (fourth state of matter).
Q5 (viii): Which form of matter do most of the material things in this world belong to?
Ans: Mixtures (homogeneous or heterogeneous).
Constructed Response Questions (Included from Exercise)
Q1 (iii): Most of the molecules we study in biochemistry are organic in nature. Where does the difference exist in organic and biochemistry branches?
Ans: Organic chemistry studies all carbon compounds and their reactions. Biochemistry studies only those carbon compounds that are involved in life processes inside living organisms.
🔬 Chapter 2: Atomic Structure
Short Questions
Q1 (i): Why is it said that almost all the mass of an atom is concentrated in its nucleus?
Ans: Because protons and neutrons (which have most of the mass) are present in the nucleus. Electrons have very little mass.
Q2 (ii): Why are elements different from one another?
Ans: Because each element has a different number of protons, electrons, and neutrons. This changes their properties.
Q3 (iii): How many neutrons are present in ^{210}_{83}Bi?
Ans: Neutrons = Mass number – Atomic number = 210 – 83 = 127 neutrons.
Constructed Response Questions
Q1 (i): Why does the energy of electron increase as we move from first shell to second shell?
Ans: The second shell is farther from the nucleus, so the attraction between nucleus and electron is weaker. The electron has higher energy.
Q2 (ii): Why is it needed to lower the pressure of the gas inside the discharge tube?
Ans: At low pressure, gas molecules are far apart. This allows the electrons to travel without colliding with gas molecules, so they can produce cathode rays.
Q3 (iii): What is the classical concept of an electron? How has this concept changed with time?
Ans: Classical concept: electron is a tiny solid particle moving in fixed paths. Modern concept: electron is a charged cloud with wave-like nature, and its exact position cannot be determined (uncertainty principle).
⚛️ Chapter 3: Chemical Bonding
Q1 (i): What type of elements lose their outer electron easily and what type gain electrons easily?
Ans: Metals (especially alkali metals) lose electrons easily. Non-metals (especially halogens) gain electrons easily.
Q2 (iii): Give one example of an element which exists as a crystalline solid and has covalent bonds between its atoms.
Ans: Diamond (carbon) or silicon dioxide (sand).
Q3 (v): Is coordinate covalent bond a strong bond?
Ans: Yes, once formed it behaves like a normal covalent bond and is strong.
Q4 (vi): Write down dot and cross formula of HNO₃.
Ans: (Student should draw: H – O – N(=O) – O with dots and crosses; nitrogen shares with three oxygens, one O is bonded to H.)
Constructed Response Questions
Q1 (i): Why HF is a liquid while HCl is a gas?
Ans: HF molecules form strong hydrogen bonds with each other due to high electronegativity of fluorine. HCl has weaker intermolecular forces, so it is a gas.
Q2 (ii): Why covalent compounds are generally not soluble in water?
Ans: Most covalent compounds are non-polar, while water is polar. "Like dissolves like" – non-polar substances do not dissolve in polar solvents.
Q3 (iii): How do metals conduct heat?
Ans: Heat energy makes free electrons move faster. These mobile electrons transfer heat rapidly throughout the metal.
Q4 (iv): How many oxides does nitrogen form? Write their formulae.
Ans: Nitrogen forms five oxides: N₂O, NO, N₂O₃, NO₂, N₂O₅.
📊 Chapter 4: Stoichiometry
Short Questions (Included from Exercise)
Q1 (i): Write down the chemical formula of barium nitride.
Ans: Ba₃N₂.
Q2 (iii): How many molecules are present in 1.5 g H₂O?
Ans: Moles = 1.5/18 = 0.0833. Molecules = 0.0833 × 6.022×10²³ = 5.01×10²² molecules.
Q3 (iv): What is the difference between a mole and Avogadro's number?
Ans: A mole is the amount of substance containing Avogadro's number of particles. Avogadro's number (6.022×10²³) is the number of particles in one mole.
Q4 (v): Write the chemical equation for: Copper + Sulphuric acid → Copper sulphate + Sulphur dioxide + Water.
Ans: Cu + 2H₂SO₄ → CuSO₄ + SO₂ + 2H₂O.
Constructed Response Questions
Q1 (i): Different compounds will never have the same molecular formula but they can have the same empirical formula. Explain.
Ans: Molecular formula shows actual number of atoms. Different compounds have different atom counts. Empirical formula shows simplest ratio. Example: C₆H₆ and C₂H₂ both have empirical formula CH.
Q2 (ii): Write down the chemical formulas of: Calcium phosphate, Aluminium nitride, Sodium acetate, Ammonium carbonate, Bismuth sulphate.
Ans:
· Calcium phosphate: Ca₃(PO₄)₂
· Aluminium nitride: AlN
· Sodium acetate: CH₃COONa
· Ammonium carbonate: (NH₄)₂CO₃
· Bismuth sulphate: Bi₂(SO₄)₃
🔥 Chapter 5: Energetics
Q1 (i): What is the difference between enthalpy and enthalpy change?
Ans: Enthalpy (H) is the total heat content of a system. Enthalpy change (ΔH) is the amount of heat absorbed or released during a reaction.
Q2 (ii): Why is breaking of a bond an endothermic process?
Ans: Energy is needed to overcome the attractive forces holding atoms together. So energy is absorbed.
Q3 (iii): Depict the transition state for the reaction H₂ + Cl₂ → 2HCl.
Ans: (Student should draw a diagram showing H–H and Cl–Cl bonds breaking and H–Cl bonds forming in an intermediate state.)
Q4 (v): What is the role of glycogen in our body?
Ans: Glycogen is stored in the liver and muscles. When the body needs energy, glycogen breaks down into glucose to provide energy.
Constructed Response Questions
Q1 (ii): Explain why the reaction between oxygen and nitrogen does not take place under normal conditions, but in lightning they react to give NO. The reaction stops as soon as lightning stops.
Ans: The reaction N₂ + O₂ → 2NO is highly endothermic (absorbs 180.6 kJ). Normal conditions do not provide enough energy. Lightning provides high energy, so the reaction occurs. When lightning stops, energy is no longer available, so reaction stops.
Q2 (iii): A reaction between natural gas (CH₄) and atmospheric oxygen does not take place when you mix them. As soon as you show a burning match stick, the reaction starts immediately and continues until one reactant is used up. Explain.
Ans: The reaction has a high activation energy. A burning match provides the initial energy (activation energy) to start the reaction. Once started, the reaction releases heat (exothermic), which keeps it going.
⚖️ Chapter 6: Equilibria
Q1 (i): How is dynamic equilibrium different from static equilibrium?
Ans: In static equilibrium, nothing moves or changes. In dynamic equilibrium, reactions continue in both directions at equal rates, so there is no net change.
Q2 (iii): How can you get the maximum yield in a reversible reaction?
Ans: By removing one of the products as soon as it is formed (e.g., letting a gas escape). This forces the reaction to keep moving forward.
Q3 (iv): How can you decrease the time to reach equilibrium in a reversible reaction?
Ans: By using a catalyst. A catalyst speeds up both forward and backward reactions equally, so equilibrium is reached faster.
Q1 (i): Why are some reactions irreversible while others are reversible?
Ans: Irreversible reactions go to completion because one product escapes as gas or forms a precipitate, or because products are very stable. Reversible reactions occur in closed containers where products can recombine.
Q2 (ii): Why are combustion reactions generally irreversible?
Ans: Because the products (CO₂ and H₂O) are very stable and do not recombine to form the original fuel and oxygen.
Q3 (iii): Can you make an irreversible reaction reversible and vice versa?
Ans: Yes, by changing conditions. Example: CaCO₃ decomposition is reversible in a closed container (CaO + CO₂ ⇌ CaCO₃) but irreversible in an open container where CO₂ escapes.
🧪 Chapter 7: Acid Base Chemistry
Q1 (i): Choose Arrhenius acids among: HF, NH₄, H₂SO₃, SO₃, H₂S, H₂O.
Ans: HF, H₂SO₃, H₂S, H₂O (H₂O gives H⁺ and OH⁻ so can act as both).
Q2 (iii): Which salt is formed when HCl reacts with BaCO₃?
Ans: Barium chloride (BaCl₂).
Q3 (iv): How will you justify that HSO₄⁻ is a Bronsted-Lowry acid?
Ans: HSO₄⁻ can donate a proton (H⁺) to become SO₄²⁻. So it is a Bronsted-Lowry acid.
Q1 (i): What chemical name will you give to soap as a compound?
Ans: Soap is sodium or potassium salt of long-chain fatty acids (e.g., sodium stearate).
Q2 (iii): Why does Na₂CO₃ behave like a base in water?
Ans: Na₂CO₃ reacts with water to produce OH⁻ ions: CO₃²⁻ + H₂O → HCO₃⁻ + OH⁻.
So it shows basic properties.
Q3 (iv): Is NaHCO₃ a base or an acid? Justify.
Ans: It is both. It can donate H⁺ (acid) and also accept H⁺ (base). It is amphoteric.
📅 Chapter 8: Periodic Table and Periodicity
Q1 (i): Why was atomic number chosen to arrange the elements in the periodic table?
Ans: Atomic number is unique for each element and determines its properties. Atomic mass was not regular and caused problems (e.g., Co and Ni).
Q2 (ii): What is the significance of the word "periodic"?
Ans: It means properties of elements repeat after regular intervals when arranged by atomic number.
Q3 (iii): Why does the size of a period increase as we move down the periodic table?
Ans: Each new period starts with a new shell (n increases), so more electrons can be accommodated. Number of elements = 2n².
Q4 (v): Do you expect calcium to be more reactive than sodium? Give reason.
Ans: No, sodium is more reactive. Sodium has one valence electron and loses it more easily. Calcium has two electrons but requires more energy to remove them.
Q5 (vi): Which element has the maximum atomic radius and which has the minimum in third period?
Ans: Maximum: Sodium (Na); Minimum: Argon (Ar) – but noble gases have larger radii due to different measurement method; among non-noble gases, Chlorine (Cl) is smallest.
Q6 (vii): Why are the most electronegative elements present in groups 16 and 17?
Ans: They have high nuclear charge and small atomic size. They need only 1 or 2 electrons to complete octet, so they attract electrons strongly.
Q7 (viii): The first ionization energy of magnesium is less than the second one. Give reason.
Ans: First electron is removed from a neutral atom. Second electron is removed from a positive ion (Mg⁺), which has stronger attraction on remaining electrons, so more energy is needed.
Q8 (ix): Is it possible for two metals or two non-metals to form an ionic bond?
Ans: No. Ionic bonds form between metal and non-metal. Two metals form metallic bond. Two non-metals form covalent bond.
Q9 (x): Which element has the least value of ionization energy and which has the highest value of electronegativity?
Ans: Least ionization energy: Cesium (Cs) among metals; Highest electronegativity: Fluorine (F).
Constructed Response Questions
Q1 (i): Suppose a new element is discovered. Where would you place it in the periodic table?
Ans: By determining its atomic number (number of protons) and electronic configuration. Then find its period (shell number) and group (valence electrons).
Q2 (ii): What is the first element of the periodic table? Will it lose or gain an electron?
Ans: Hydrogen (H). It can both lose to become H⁺ or gain to become H⁻. It behaves uniquely.
Q3 (iii): Atomic radii of boron and aluminium are 88 pm and 125 pm respectively. Which element loses electrons easily?
Ans: Aluminium (Al) has larger atomic radius, so its valence electrons are farther from nucleus and easier to remove.
Q4 (iv): How would you find the atomic radius of an atom?
Ans: Atomic radius is half the distance between the nuclei of two identical bonded atoms (e.g., in Cl₂ molecule).
Q5 (v): Why is it not possible for oxygen to form O³⁻ like nitrogen forms N³⁻?
Ans: Oxygen has 6 valence electrons. It can only gain 2 electrons to complete octet. Adding a third electron would require much energy due to strong repulsion.
🌍 Chapter 9: Group Properties and Elements
Q1 (i): Why does it become easier to cut an alkali metal when we move from top to bottom in group I?
Ans: Down the group, metallic bond strength decreases because atomic size increases. So metals become softer and easier to cut.
Q2 (ii): Predict the reactivity of potassium towards halogens.
Ans: Potassium is highly reactive. It will react violently with halogens to form potassium halides (e.g., KCl, KBr).
Q3 (iii): In the reaction Cl₂ + 2NaBr → 2NaCl + Br₂, which is the reducing agent?
Ans: NaBr is the reducing agent (Br⁻ loses electron and is oxidized to Br₂).
Q4 (iv): Why does iodine exist in the solid state at room temperature?
Ans: Iodine has large atoms with many electrons, so intermolecular forces (London dispersion forces) are strong enough to keep it solid.
Q5 (v): How does nickel catalyze the hydrogenation of oil?
Ans: Nickel adsorbs hydrogen gas on its surface, breaking H–H bonds. It also adsorbs oil molecules, bringing them close so hydrogen adds across double bonds.
Constructed Response Questions
Q1 (i): Which noble gas should have the lowest boiling point and why?
Ans: Helium (He) has the lowest boiling point because it has the smallest atomic size and very weak London forces.
Q2 (ii): Compare the reactions of alkali metals with chlorine.
Ans: All react vigorously to form metal chlorides (2M + Cl₂ → 2MCl). Reactivity increases down the group: Li reacts slowly, Na vigorously, K violently, Rb and Cs explode.
Q3 (iv): Name any three elements in the periodic table which exist as liquids.
Ans: Mercury (Hg), Bromine (Br₂), Gallium (Ga – melts at 29.8°C, liquid on a hot day).
Q4 (v): Why are transition elements different from normal elements?
Ans: Transition elements have partially filled d-subshells, show variable oxidation states, form colored compounds, and act as catalysts.
Q5 (vi): Compare the reactivity of chlorine and bromine as oxidizing agents.
Ans: Chlorine is a stronger oxidizing agent than bromine because it has smaller size and higher electronegativity. Chlorine can displace bromine from bromides.
Q6 (vii): Which element is the most reactive and which is the least reactive among halogens? Give two reasons.
Ans: Most reactive: Fluorine (F). Least reactive: Iodine (I). Reasons: As size increases, tendency to gain electron decreases. Also electronegativity decreases down the group.
🌿 Chapter 10: Environmental Chemistr
Q1 (i): What is the main objective of environmental education? (From textbook)
Ans: To enlighten people (especially students) about the importance of protecting and conserving our environment.
Q2 (iv): What are the harmful effects of carbon monoxide?
Ans: CO binds with hemoglobin in blood, stopping it from carrying oxygen. This causes suffocation, headaches, dizziness, and can lead to death.
Q3 (v): Differentiate between an organic and an inorganic compound.
Ans: Organic compounds contain carbon (except simple salts like carbonates, bicarbonates, oxides, carbides). Inorganic compounds contain little or no carbon.
Constructed Response Questions
Q1 (i): How is air pollution affected by plants? (Paraphrased – actual question may be: How do plants help reduce air pollution?)
Ans: Plants absorb CO₂ during photosynthesis and release O₂. They also trap particulate matter on their leaves and surfaces, cleaning the air.
🧴 Chapter 11: Hydrocarbons
Q1 (i): Define hydrocarbon and give two examples.
Ans: Hydrocarbons are compounds containing only carbon and hydrogen. Examples: methane (CH₄), ethane (C₂H₆).
Q2 (ii): Distinguish between alkane and alkene.
Ans: Alkanes have only single bonds (saturated) – general formula CₙH₂ₙ₊₂. Alkenes have at least one double bond (unsaturated) – general formula CₙH₂ₙ.
Q3 (iv): Write the structural formulas of methane and ethene.
Ans: Methane: H–C–H with four H's (tetrahedral). Ethene: H₂C=CH₂ (double bond).
Q4 (v): What is the general formula of alkynes? Give one example.
Ans: General formula CₙH₂ₙ₋₂. Example: ethyne (C₂H₂).
Q5 (vi): Why are alkenes called unsaturated hydrocarbons?
Ans: Because they contain double bonds, so carbon atoms are not bonded to the maximum number of hydrogen atoms.
Q6 (vii): How is ethene prepared from ethanol?
Ans: Ethanol is heated with excess concentrated H₂SO₄ at 170°C to produce ethene and water: C₂H₅OH → C₂H₄ + H₂O.
Constructed Response Questions
Q1 (i): Describe the preparation of methane in the laboratory.
Ans: Methane is prepared by heating sodium acetate with soda lime (NaOH + CaO). Reaction: CH₃COONa + NaOH → CH₄ + Na₂CO₃.
Q2 (ii): What is cracking? Write its types and importance.
Ans: Cracking is breaking down large hydrocarbon molecules into smaller useful ones. Types: thermal cracking and catalytic cracking. Importance: produces gasoline, diesel, and alkenes (like ethene).
Q3 (iii): Differentiate between saturated and unsaturated hydrocarbons with examples.
Ans: Saturated hydrocarbons have all single bonds (alkanes, e.g., methane). Unsaturated have double/triple bonds (alkenes/alkynes, e.g., ethene, ethyne).
Best of luck for your exams! 🧪📚
