Chemistry Guess Paper Notes 2026 Class 9th Important Questions with Answers Punjab Board ALP Smart Syllabus)
📘 Chapter 1: States of Matter and Phase Changes
Q1: Define chemistry.
Ans: Chemistry is the branch of science that deals with the composition, structure, properties, and changes of matter.
Q2: Name any three branches of chemistry.
Ans: Physical chemistry, organic chemistry, and inorganic chemistry.
Q3: Define matter. What are its three main states?
Ans: Matter is anything that has mass and occupies space. Its three main states are solid, liquid, and gas.
Q4: Differentiate between an element and a compound.
Ans: An element is a pure substance made of only one type of atom (e.g., Na). A compound is made of two or more different atoms chemically combined in a fixed ratio (e.g., H₂O).
Q5: What is a mixture? Give an example of a homogeneous mixture.
Ans: A mixture is a combination of two or more substances that are not chemically bonded. Example of homogeneous mixture: salt solution.
Q6: Define saturated solution.
Ans: A solution in which no more solute can be dissolved at a given temperature is called a saturated solution.
Q7: Differentiate between a true solution and a suspension.
Ans: True solution is homogeneous, particles cannot be seen and do not settle (e.g., salt in water). Suspension is heterogeneous, particles are visible and settle down (e.g., chalk in water).
Q8: Why are gases easily compressible but liquids are not?
Ans: Gases have large intermolecular spaces and weak forces, so particles can be pushed closer. Liquids have smaller spaces and stronger forces, so they are almost incompressible.
🔬 Chapter 2: Atomic Structure
Q1: Why is an atom electrically neutral?
Ans: Because the number of protons (positive charge) equals the number of electrons (negative charge) in an atom.
Q2: Define atomic number and mass number.
Ans: Atomic number (Z) is the number of protons in the nucleus. Mass number (A) is the sum of protons and neutrons.
Q3: Calculate the number of neutrons in ^{210}_{83}Bi.
Ans: Number of neutrons = Mass number – Atomic number = 210 – 83 = 127 neutrons.
Q4: Why does the energy of an electron increase when it moves from first shell to second shell?
Ans: Because the second shell is farther from the nucleus, so the attractive force on the electron is weaker, and it possesses higher energy.
Q5: What information did Rutherford get from his gold foil experiment?
Ans: He concluded that an atom has a tiny, dense, positively charged nucleus at its center, and most of the atom is empty space.
Q6: State Bohr’s atomic model.
Ans: Electrons revolve around the nucleus in fixed circular paths called shells or orbits. Each shell has a fixed energy. Electrons can jump between shells by absorbing or emitting energy.
Q7: What is the maximum number of electrons that can be accommodated in K, L, and M shells?
Ans: K shell: 2 electrons, L shell: 8 electrons, M shell: 18 electrons (using 2n² formula).
Q8: What are isotopes? Give an example.
Ans: Atoms of the same element with the same atomic number but different mass numbers. Example: Carbon-12 and Carbon-14.
⚛️ Chapter 3: Chemical Bonding
Q1: Why do atoms form chemical bonds?
Ans: Atoms form bonds to achieve stability by completing their outermost shell (octet or duplet) and lowering their energy.
Q2: Define ionic bond with an example.
Ans: A bond formed by complete transfer of electrons from a metal to a non-metal. Example: NaCl (Na⁺ and Cl⁻).
Q3: Define covalent bond with an example.
Ans: A bond formed by mutual sharing of electrons between atoms. Example: H₂O.
Q4: Why is graphite a good conductor of electricity?
Ans: Graphite has a layered structure with free mobile electrons between the layers that can move and conduct electricity.
Q5: Why are covalent compounds generally insoluble in water?
Ans: Covalent compounds are non-polar or weakly polar, while water is a polar solvent. Like dissolves like, so they do not mix.
Q6: How does metallic bonding explain the malleability of metals?
Ans: In metallic bonding, positive ions are surrounded by a sea of mobile electrons. When force is applied, layers of ions can slide over each other without breaking the bond.
Q7: Define coordinate covalent bond with an example.
Ans: A bond in which the shared pair of electrons is donated by only one atom. Example: NH₄⁺.
Q8: Why are ionic compounds usually solids with high melting points?
Ans: Because they have strong electrostatic forces of attraction between oppositely charged ions, requiring a lot of energy to break.
📊 Chapter 4: Stoichiometry
Q1: What is Avogadro’s number? Write its value.
Ans: Avogadro’s number is the number of particles (atoms, molecules, or ions) in one mole of a substance. Its value is 6.022 \times 10^{23}.
Q2: Differentiate between molecular formula and empirical formula.
Ans: Molecular formula shows the actual number of atoms in a molecule (e.g., H₂O₂). Empirical formula shows the simplest whole number ratio (e.g., HO).
Q3: Calculate the number of moles in 36 g of water (H₂O). (Atomic masses: H=1, O=16)
Ans: Molar mass of H₂O = 18 g/mol. Number of moles = given mass / molar mass = 36/18 = 2 moles.
Q4: Define a mole.
Ans: A mole is the amount of substance that contains Avogadro’s number (6.022 \times 10^{23}) of particles.
Q5: Write the chemical formula of calcium phosphide.
Ans: Ca₃P₂.
Q6: Why is the mole concept important?
Ans: It allows us to count atoms and molecules by weighing, because atoms are too small to count individually.
Q7: What is the empirical formula of benzene (C₆H₆)?
Ans: CH.
Q8: Calculate the number of molecules in 1.5 g of H₂O.
Ans: Moles = 1.5/18 = 0.0833 moles. Number of molecules = 0.0833 × 6.022×10²³ = 5.02×10²² molecules.
🔥 Chapter 5: Energetics
Q1: Define activation energy.
Ans: The minimum amount of energy required by reactant particles to start a chemical reaction.
Q2: Why is breaking a chemical bond endothermic?
Ans: Because energy must be absorbed to overcome the attractive forces holding the atoms together.
Q3: Differentiate between exothermic and endothermic reactions with an example of each.
Ans: Exothermic reactions release heat (e.g., burning of methane). Endothermic reactions absorb heat (e.g., photosynthesis).
Q4: What is the role of glycogen in the human body?
Ans: Glycogen is stored in the liver and muscles and provides energy when the body needs it (as a reserve fuel).
Q5: Define enthalpy change (ΔH).
Ans: The amount of heat absorbed or released during a chemical reaction at constant pressure.
Q6: Why does bond formation release energy?
Ans: When atoms bond, they become more stable and release excess energy in the form of heat.
Q7: What is aerobic respiration?
Ans: The process of breaking down glucose in the presence of oxygen to release energy, carbon dioxide, and water.
Q8: Draw an energy profile diagram for an exothermic reaction. (Conceptual)
Ans: (Students should draw reactants at higher energy level than products, with activation energy peak in between.)
⚖️ Chapter 6: Equilibria
Q1: Define reversible reaction with an example.
Ans: A reaction that can proceed in both forward and backward directions under the same conditions. Example: N_2 + 3H_2 \rightleftharpoons 2NH_3.
Q2: What is dynamic equilibrium?
Ans: A state in a reversible reaction where the rate of the forward reaction equals the rate of the backward reaction, so concentrations of reactants and products remain constant.
Q3: Why can’t a reversible reaction reach equilibrium in an open container?
Ans: Because products (especially gases) escape, preventing the backward reaction from occurring.
Q4: How can you increase the yield of a reversible reaction?
Ans: By removing one or more products as they are formed (e.g., letting a gas escape).
Q5: Give an example of a physical reversible change from the textbook.
Ans: Heating blue copper(II) sulfate pentahydrate turns it white; adding water turns it blue again.
Q6: What does the symbol mean?
Ans: It means the reaction is reversible.
Q7: Why are combustion reactions generally irreversible?
Ans: Because the products (CO₂, H₂O) are very stable and do not recombine to form the original reactants.
🧪 Chapter 7: Acid Base Chemistry
Q1: Define Arrhenius acid and base with examples.
Ans: An acid gives H⁺ ions in water (e.g., HCl). A base gives OH⁻ ions in water (e.g., NaOH).
Q2: Why is HCl a strong acid but acetic acid is a weak acid?
Ans: HCl completely ionizes in water, while acetic acid only partially ionizes.
Q3: How many OH⁻ ions are released by Ca(OH)₂ in water?
Ans: Two OH⁻ ions per formula unit.
Q4: Write the reaction of dilute HCl with zinc granules.
Ans: Zn + 2HCl --------------> ZnCl_2 + H_2 (hydrogen gas is produced).
Q5: What happens when NH₄Cl reacts with NaOH? Write the reaction.
Ans: NH_4Cl + NaOH ------------> NaCl + H_2O + NH_3 (ammonia gas is released).
Q6: Define neutralization reaction.
Ans: The reaction between an acid and a base to produce salt and water.
Q7: Write the reaction of sodium carbonate with hydrochloric acid.
Ans: Na2CO3 + 2HCl -------------> 2NaCl + H2O + CO2.
Q8: What is an alkali? Give an example.
Ans: A base that is soluble in water is called an alkali. Example: NaOH.
📅 Chapter 8: Periodic Table and Periodicity
Q1: State the modern periodic law.
Ans: Properties of elements are a periodic function of their atomic numbers.
Q2: Why do elements in the same group have similar chemical properties?
Ans: Because they have the same number of electrons in their outermost shell (valence electrons).
Q3: Arrange Li, Be, B, C in increasing order of atomic radius. Give reason.
Ans: C < B < Be < Li. Atomic radius decreases across a period because nuclear charge increases, pulling electrons closer.
Q4: Why does ionization energy decrease down a group?
Ans: Atomic size increases down a group, so the outermost electron is farther from the nucleus and easier to remove.
Q5: Name the most electronegative element.
Ans: Fluorine.
Q6: Define electronegativity.
Ans: The ability of an atom to attract shared electrons in a covalent bond.
Q7: What is the difference between a period and a group?
Ans: A period is a horizontal row, and a group is a vertical column in the periodic table.
Q8: Which element has the largest atomic radius in period 3?
Ans: Sodium (Na).
🌍 Chapter 9: Group Properties and Elements
Q1: Why are alkali metals stored under oil?
Ans: They are highly reactive with air and moisture; oil prevents contact with oxygen and water.
Q2: Why does reactivity of halogens decrease down the group?
Ans: Atomic size increases, so the tendency to gain an electron decreases.
Q3: Name a transition metal used as a catalyst in Haber’s process.
Ans: Iron (Fe).
Q4: Give two physical properties of transition metals.
Ans: They have high melting points and high densities.
Q5: Why is iodine solid at room temperature but fluorine is gas?
Ans: Iodine has larger atoms and stronger intermolecular forces (London dispersion forces) due to more electrons.
Q6: What are noble gases? Why are they unreactive?
Ans: Noble gases are Group 18 elements. They are unreactive because their outermost shell is complete (octet).
Q7: Write the reaction of sodium with water.
Ans: 2Na + 2H2O ---------> 2NaOH + H2.
Q8: What is the color of chlorine gas?
Ans: Yellowish-green.
🌿 Chapter 10: Environmental Chemistry
Q1: Name two major air pollutants and their sources.
Ans: Carbon monoxide (from incomplete combustion of fuels) and sulfur dioxide (from burning fossil fuels containing sulfur).
Q2: What is acid rain? Write two harmful effects.
Ans: Acid rain is rain with pH below 5.6 due to SO₂ and NO₂. Effects: damages buildings (marble) and harms aquatic life.
Q3: How does carbon monoxide harm human health?
Ans: CO binds with hemoglobin in blood more strongly than oxygen, reducing oxygen supply to body tissues.
Q4: Why are catalytic converters used in vehicles?
Ans: They convert harmful gases (CO, NOₓ, unburned hydrocarbons) into less harmful CO₂, N₂, and H₂O.
Q5: What is the percentage of nitrogen in clean dry air?
Ans: Approximately 78%.
Q6: Define air pollutant.
Ans: Any substance in the air that has harmful effects on humans, animals, plants, or the environment.
Q7: Write the reaction of formation of acid rain from SO₂.
Ans: 2SO2 + O2 ---------> 2SO_3;
SO3 + H2O ----------> H2SO4.
Q8: What is photochemical smog?
Ans: It is a mixture of smoke, fog, and pollutants (like nitrogen oxides and volatile organic compounds) formed in the presence of sunlight.
🧴 Chapter 11: Hydrocarbons
Q1: Define hydrocarbon. Classify with examples.
Ans: Compounds containing only carbon and hydrogen. Classification: saturated (alkanes, e.g., methane) and unsaturated (alkenes, e.g., ethene; alkynes, e.g., ethyne).
Q2: Write the molecular formula of methane, ethane, and ethene.
Ans: Methane CH₄, ethane C₂H₆, ethene C₂H₄.
Q3: Why are alkanes called saturated hydrocarbons?
Ans: Because they contain only single carbon-carbon bonds, and all carbon atoms are bonded to the maximum number of hydrogen atoms.
Q4: What is the general formula of alkenes?
Ans: CₙH₂ₙ.
Q5: Name the simplest alkene and write its structural formula.
Ans: Ethene (C₂H₄). Structural formula: H₂C=CH₂.
Q6: What is the difference between an alkane and an alkene?
Ans: Alkanes have only single bonds and are saturated; alkenes have at least one double bond and are unsaturated.
Q7: Write the complete combustion reaction of methane.
Ans: CH4 + 2O2 -------> CO2 + 2H2O.
Q8: What is the functional group of alkenes?
Ans: Carbon-carbon double bond (>C=C<).
✅ Final Instructions for Students
· Memorize answers exactly as given – they are textbook‑aligned.
· Practice numericals – especially from Chapter 4 (mole, empirical formula) and Chapter 2 (neutron calculation).
· Learn reactions – acid + metal, acid + carbonate, base + ammonium salt, combustion.
· Understand trends – atomic radius, ionization energy, electronegativity, reactivity in groups & periods.
· Skip excluded topics completely as per ALP 2025–26.
