Long Questions Guess Paper and Notes Chemistry New 9th 2026 Smart Syllabus
( Note: for Short Questions click here)
📘 Chapter 1: States of Matter and Phase Changes
Long Question 1: Differentiate between elements, compounds, and mixtures.
Answer:
Element
· An element is the simplest form of matter. It is a pure substance containing the same kind of atoms.
· It cannot be broken down into simpler particles by ordinary chemical reactions.
· When an element exists as atoms, it is represented by a symbol (e.g., Na, Ca).
· Gaseous elements exist as independent molecules (e.g., N₂, O₂) except noble gases which are monatomic.
· Properties of an element are fixed.
Compound
· A compound is a pure substance formed by the chemical combination of two or more atoms of different elements in a fixed ratio (by weight).
· It can be broken into its constituent elements by a chemical reaction.
· The properties of a compound are always different from the elements from which it is formed (e.g., water is different from hydrogen and oxygen).
· Compounds exist as molecules (e.g., HCl, NH₃, H₂O) or network arrangements (e.g., NaCl, SiO₂).
Mixture
· A mixture is an impure substance formed by mixing two or more elements or compounds in any ratio.
· Each component retains its identity and specific properties.
· A mixture may be homogeneous (e.g., salt solution) or heterogeneous (e.g., rock).
· Components are not chemically bound and can be separated by physical methods.
· The properties of a mixture are the sum of the properties of its components.
Long Question 3: What is a solution? Explain types of solutions with examples.
Answer:
Definition: A solution is a homogeneous mixture of two or more substances.
Types of Solutions:
1. True Solution
· Particle size is less than 1 nm.
· Particles cannot be seen with the naked eye.
· Does not scatter light.
· Particles do not settle down.
· Passes through filter paper without leaving residue.
· Example: salt solution, sugar solution.
2. Colloidal Solution (Colloid)
· Particle size between 1 nm and 1000 nm.
· Particles are visible under a microscope.
· Scatters light (Tyndall effect).
· Particles do not settle down (stable).
· Passes through filter paper but not through animal membrane.
· Example: starch solution, milk, fog.
3. Suspension
· Particle size greater than 1000 nm.
· Particles are visible to the naked eye.
· Does not scatter light.
· Particles settle down on standing.
· Does not pass through filter paper; residue remains.
· Example: chalk powder in water, muddy water.
Long Question 4: What are the main branches of chemistry? Briefly describe any five.
Answer:
Chemistry is divided into many branches. Five important branches are:
1. Physical Chemistry
· It investigates how substances behave at atomic and molecular levels.
· It explains how fundamental physical laws cause atoms and molecules to show specific characteristics.
· It is used to predict and change the rates of reactions.
2. Organic Chemistry
· It deals with carbon compounds (hydrocarbons and their derivatives) except simple salts like carbonates, bicarbonates, oxides, and carbides.
· We study the structure, formation, properties, composition, and reactions of carbon-containing compounds.
· Organic compounds are found in all forms of life.
3. Inorganic Chemistry
· It is the study of the synthesis, composition, properties, and structure of elements and compounds that contain little or no carbon.
· Inorganic compounds include metals, non-metals, salts, acids, and bases.
· They are used as fertilizers, medicines, catalysts, pigments, and coatings.
4. Environmental Chemistry
· It is the scientific study of chemical and biochemical phenomena that occur on Earth.
· It studies the sources, reactions, effects, and fates of chemical species in air, soil, and water.
· It helps in understanding the causes, effects, and solutions of different types of pollution.
5. Biochemistry
· It is the branch of chemistry that understands life through chemical processes.
· It studies chemical substances and vital processes occurring in living organisms.
· It provides insights into the structure and function of molecules such as proteins, carbohydrates, lipids, and nucleic acids.
🔬 Chapter 2: Atomic Structure
Long Question 1: Describe the discovery of electron, proton, and neutron.
Answer:
1. Discovery of Electron (J.J. Thomson, 1897)
· Experiment used a discharge tube (glass tube with two metallic electrodes, very low pressure, high voltage).
· Observation: Cathode rays were produced from the cathode and travelled towards the anode.
· When passed through an electric field, cathode rays bent towards the positive plate, showing they carry negative charge.
· They were also deflected by a magnetic field.
· Thomson calculated the charge-to-mass ratio and proved that cathode rays are negatively charged material particles.
· These particles were named electrons.
2. Discovery of Proton (E. Goldstein, 1886; Rutherford, 1917)
· Goldstein used a discharge tube with a perforated (holes) cathode.
· He observed new rays (canal rays or anode rays) moving from the anode towards the cathode and passing through the holes.
· These rays were positively charged because they bent towards the negative plate.
· Their properties varied depending on the gas used.
· In 1917, Rutherford proved that the hydrogen nucleus (proton) is present in all other nuclei.
· Proton is positively charged and 1836 times heavier than an electron.
3. Discovery of Neutron (James Chadwick, 1932)
· Chadwick bombarded beryllium with alpha particles.
· He observed neutral radiations that were not deflected by electric or magnetic fields.
· These particles had mass nearly equal to a proton but no charge.
· He named them neutrons.
· Neutrons are present in all atoms except ordinary hydrogen (protium).
Long Question 2: Explain Rutherford’s atomic model (Gold foil experiment) and its conclusions.
Answer:
Experiment:
· A very thin gold foil (about 0.00004 cm thick) was bombarded with alpha particles (positively charged).
· A zinc sulfide screen was placed around to detect the alpha particles.
Observations:
1. Most alpha particles passed straight through the foil.
2. Some were deflected by small angles.
3. Very few (about 1 in 20,000) were deflected back at large angles (more than 90°).
Conclusions (Rutherford’s Atomic Model):
1. Most of the atom is empty space (because most alpha particles passed through).
2. The atom has a tiny, dense, positively charged center called the nucleus (this caused the large deflections).
3. The nucleus is very small (about 1/100,000 the size of the atom) but contains almost all the mass of the atom.
4. Electrons revolve around the nucleus in circular paths.
Limitations of Rutherford’s Model:
· Could not explain the stability of the atom (revolving electrons should lose energy and fall into the nucleus).
· Could not explain the line spectra of atoms.
Long Question 3: Explain Bohr’s atomic model.
Answer:
Niels Bohr (1913) proposed a model for the hydrogen atom to overcome the limitations of Rutherford’s model.
Main Postulates (Key Points):
1. Orbits (Shells): Electrons revolve around the nucleus in fixed circular paths called orbits or shells. These are also called energy levels and are named K, L, M, N, etc.
2. Fixed Energy: As long as an electron remains in a particular shell, its energy remains constant (does not radiate energy).
3. No intermediate paths: An electron cannot exist between two shells.
4. Ground state: The shell closest to the nucleus (K shell) has the lowest energy. This is the normal state of the atom.
5. Excited state: When an electron absorbs energy, it jumps to a higher shell. This is called the excited state.
6. Emission of energy: When an electron jumps from a higher shell to a lower shell, it emits energy in the form of light or heat.
Formula for maximum electrons in a shell: 2n^2 (where n = shell number).
· K shell (n=1): maximum 2 electrons
· L shell (n=2): maximum 8 electrons
· M shell (n=3): maximum 18 electrons
· N shell (n=4): maximum 32 electrons
Significance of Bohr’s Model:
· Successfully explained the stability of the atom.
· Explained the hydrogen line spectrum.
· Introduced the concept of quantized energy levels.
Limitation: Could not explain the spectra of larger atoms (more than one electron).
Long Question 4: Define atomic number, mass number, and isotopes. How are they related?
Answer:
1. Atomic Number (Z)
· The number of protons in the nucleus of an atom.
· It is unique for each element.
· For a neutral atom, the number of electrons equals the atomic number.
· Example: Carbon has Z=6 (6 protons and 6 electrons).
2. Mass Number (A)
· The total number of protons and neutrons in the nucleus.
· Also called nucleon number.
· Formula: A = Z + N (where N = number of neutrons).
· Example: Carbon-12 has mass number 12 (6 protons + 6 neutrons).
3. Isotopes
· Atoms of the same element having the same atomic number (Z) but different mass numbers (A).
· They have the same number of protons but different numbers of neutrons.
· Example: Hydrogen has three isotopes:
· Protium (^1_1H) – 0 neutrons
· Deuterium (^2_1H) – 1 neutron
· Tritium (^3_1H) – 2 neutrons
· Isotopes have the same chemical properties (same number of electrons) but different physical properties (mass, density, etc.).
Relationship:
· Number of neutrons = Mass number – Atomic number
· Example: ^{35}_{17}Cl has 35 – 17 = 18 neutrons.
📅 Chapter 8: Periodic Table and Periodicity
Long Question 1: Describe the modern periodic table. How are elements arranged in it?
Answer:
The modern periodic table is based on the atomic number of elements, arranged in increasing order.
Modern Periodic Law: "Properties of elements are a periodic function of their atomic numbers."
Main Features:
1. Periods (Horizontal Rows)
· There are 7 periods.
· Each period starts with an alkali metal and ends with a noble gas.
· The number of elements in a period equals the maximum number of electrons that can be accommodated in that shell (2n²).
· Period 1: 2 elements (H, He)
· Period 2 and 3: 8 elements each
· Period 4 and 5: 18 elements each
· Period 6 and 7: 32 elements each (lanthanides and actinides placed separately at the bottom)
2. Groups (Vertical Columns)
· There are 18 groups.
· Elements in the same group have the same number of valence electrons (electrons in the outermost shell).
· They show similar chemical properties.
· Some groups have family names:
· Group 1: Alkali metals
· Group 2: Alkaline earth metals
· Group 17: Halogens
· Group 18: Noble gases
3. Blocks
· s-block: Groups 1 and 2 (valence electrons in s-subshell)
· p-block: Groups 13 to 18 (valence electrons in p-subshell)
· d-block: Groups 3 to 12 (transition elements)
· f-block: Lanthanides and actinides (placed separately at the bottom)
Long Question 2: Explain periodicity in atomic radius, ionization energy, and electronegativity.
Answer:
1. Atomic Radius
· Definition:
Half the distance between the nuclei of two identical bonded atoms. It is expressed in picometers (pm).
· Trend across a period (left to right): Decreases.
Reason:
Nuclear charge (number of protons) increases, so the nucleus pulls electrons closer.
Example (period 2): Li (152 pm) → Be (113 pm) → B (88 pm) → C (77 pm) → N (75 pm) → O (73 pm) → F (71 pm) → Ne (69 pm).
· Trend down a group (top to bottom): Increases.
Reason:
New shells are added, so the outermost electrons are farther from the nucleus.
Example (group 1): Li (152 pm) → Na (186 pm) → K (227 pm) → Rb (248 pm) → Cs (265 pm).
2. Ionization Energy
Definition: The amount of energy required to remove the most loosely bound electron from an isolated gaseous atom. It is expressed in kJ/mol.
· Trend across a period:
Increases.
Reason: Atomic radius decreases, so electrons are held more tightly by the nucleus.
Example
(period 2): Li (520) → Be (899) → B (801) → C (1086) → N (1402) → O (1314) → F (1681) → Ne (2081) kJ/mol.
Trend down a group:
Decreases.
Reason:
Atomic radius increases, so the outermost electron is farther from the nucleus and easier to remove.
Example (group 1): Li (520) → Na (496) → K (419) → Rb (403) → Cs (377) kJ/mol.
3. Electronegativity
Definition:
The ability of an atom to attract the shared pair of electrons towards itself in a covalent bond.
Trend across a period:
Increases.
Reason:
Nuclear charge increases, so the attraction for shared electrons increases.
Example
(period 2): Li (1.0) → Be (1.6) → B (2.0) → C (2.6) → N (3.0) → O (3.4) → F (4.0) (on Pauling scale).
· Trend down a group: Decreases.
Reason:
Atomic size increases, so the shared electrons are farther from the nucleus and less attracted.
Example
(group 17): F (4.0) → Cl (3.2) → Br (3.0) → I (2.7).
· Most electronegative element: Fluorine (4.0).
Long Question 3: Why do elements in the same group show similar chemical properties? Explain with examples.
Answer:
Elements in the same group have the same number of valence electrons (electrons in the outermost shell). Chemical properties depend largely on the number and arrangement of valence electrons. Therefore, they show similar chemical behavior.
Explanation with examples:
Example 1 – Group 1 (Alkali Metals)
· All have 1 valence electron (ns¹ configuration).
· They all tend to lose this one electron to form +1 ions.
· Reaction with water is similar for all:
2Li + 2H_2O \rightarrow 2LiOH + H_2
2Na + 2H_2O \rightarrow 2NaOH + H_2
2K + 2H_2O \rightarrow 2KOH + H_2
· All form hydroxides that are strong alkalis (soluble bases).
· All react with halogens to form halides: 2Na + Cl_2 \rightarrow 2NaCl.
Example 2 – Group 17 (Halogens)
· All have 7 valence electrons (ns² np⁵ configuration).
· They all tend to gain one electron to form –1 ions.
· Reaction with sodium is similar for all:
2Na + Cl_2 \rightarrow 2NaCl
2Na + Br_2 \rightarrow 2NaBr
2Na + I_2 \rightarrow 2NaI
· All form hydrogen halides (HX) when reacted with hydrogen.
· All are diatomic molecules (F₂, Cl₂, Br₂, I₂) and are colored.
Conclusion: Because they have the same valence shell electron configuration, elements in the same group undergo the same types of reactions and form similar compounds.
🌿 Chapter 10: Environmental Chemistry
Long Question 1: What are air pollutants? Describe the major air pollutants, their sources, and harmful effects.
Answer:
Definition of Air Pollutant: Any substance (solid, liquid, or gas) in the air that has harmful effects on human health, quality of life, or the natural functioning of the ecosystem.
Major Air Pollutants, Sources, and Harmful Effects:
1. Carbon Monoxide (CO)
· Source: Incomplete combustion of carbon-containing fuels (vehicles, factories, burning of wood, coal).
· Harmful Effect: Binds with hemoglobin in blood 200 times more strongly than oxygen, reducing oxygen supply to body tissues → causes headaches, dizziness, unconsciousness, and even death.
2. Carbon Dioxide (CO₂)
· Source: Complete combustion of fossil fuels, respiration, volcanic eruptions.
· Harmful Effect: Greenhouse gas → causes global warming → climate change, melting of ice caps, rising sea levels, extreme weather events.
3. Sulfur Dioxide (SO₂)
· Source: Combustion of fossil fuels that contain sulfur (coal, oil), volcanic eruptions.
· Harmful Effect: Causes acid rain, respiratory problems (asthma, bronchitis), damages plants, corrodes buildings and statues.
4. Nitrogen Oxides (NO and NO₂ – NOₓ)
· Source: High-temperature combustion in car engines, power plants, lightning.
· Harmful Effect: Causes acid rain, photochemical smog, lung damage, eye irritation, and respiratory problems.
5. Particulate Matter (dust, smoke, soot, pollens, metallic compounds)
· Source: Industrial processes, vehicle exhaust, burning of fossil fuels, construction, crop burning.
· Harmful Effect: Causes respiratory problems (asthma, lung cancer), reduces visibility (haze), makes clothes dirty, and can cause allergies.
6. Methane (CH₄)
· Source: Decomposition of vegetation, waste gases from digestion in animals (cattle), rice fields, landfills.
· Harmful Effect: Greenhouse gas (25 times more potent than CO₂) → contributes to global warming.
7. Ozone (O₃) – ground level
· Source: Formed when heat and sunlight cause reactions between nitrogen oxides (NOₓ) and volatile organic compounds (hydrocarbons) from vehicle exhaust.
· Harmful Effect: Breathing ozone causes chest pain, coughing, throat irritation, and congestion. It can damage lungs and worsen asthma.
Long Question 2: What is acid rain? How is it formed? Explain its harmful effects.
Answer:
Definition: Acid rain is rainwater that has a pH between 4.2 and 4.4 (normal rain has pH about 5.6). It contains acids such as sulfuric acid (H₂SO₄) and nitric acid (HNO₃).
Formation of Acid Rain:
1. Burning of fossil fuels (coal, oil, natural gas) releases sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) into the atmosphere.
2. SO₂ reacts with oxygen (O₂) in the air to form sulfur trioxide (SO₃):
2SO_2 + O_2 \rightarrow 2SO_3
3. SO₃ dissolves in water vapor present in the air to form sulfuric acid:
SO_3 + H_2O \rightarrow H_2SO_4
4. Nitrogen oxides (NO₂) react with water vapor to form nitric acid:
2NO_2 + H_2O \rightarrow HNO_3 + HNO_2
5. These acids mix with rain clouds and fall to the ground as acid rain, hail, snow, or fog.
Harmful Effects of Acid Rain:
1. Effect on Soil
· Acid rain increases the acidity of soil.
· It dissolves and washes away essential plant nutrients like calcium and magnesium.
· It can also dissolve toxic metals (like aluminum) naturally present in soil, which are harmful to plants.
2. Effect on Plants and Vegetation
· Acid rain damages leaves and bark of trees.
· Many plants cannot grow in acidic soil.
· It weakens trees, making them more susceptible to disease and harsh weather.
· Forest decline has been observed in many parts of the world.
3. Effect on Aquatic Life
· Acid rain falls into lakes, rivers, and streams.
· It makes the water too acidic for fish and other aquatic animals to survive.
· Many lakes and rivers in industrial regions have lost their fish populations.
4. Effect on Buildings and Monuments
· Acid rain corrodes marble, limestone, and metal structures.
· Historical monuments like the Taj Mahal (India) and the Parthenon (Greece) are deteriorating due to acid rain.
· It damages bridges, railings, and statues.
5. Effect on Human Health
· Acid rain does not directly harm humans, but the pollutants (SO₂ and NOₓ) that cause acid rain also cause respiratory problems.
· Acidic fog and smog can aggravate asthma and bronchitis.
Long Question 3: Describe the composition of clean dry air.
Answer:
Clean dry air is a mixture of gases. The percentage composition by volume is as follows:
· Nitrogen (N₂): 78.0 %
· Oxygen (O₂): 21.0 %
· Argon (Ar): 0.934 %
· Carbon Dioxide (CO₂): 0.04 %
· Other noble gases (Neon, Helium, Krypton, Xenon): Trace amounts (less than 0.002 %)
· Water vapors (H₂O): Variable (0 to 4 %) depending on humidity. Water vapor is not part of "dry" air.
Important points:
· The composition may vary slightly from place to place, season to season, and day to night.
· Human activities (burning of fuels, industrial processes) can increase the concentration of pollutants like CO₂, CO, SO₂, and NOₓ.
· Plants absorb CO₂ during photosynthesis and release oxygen, helping to maintain the balance.
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✅ Final Instructions for Students
· Memorize answers in list form – no tables to confuse you.
· Practice diagrams separately (Bohr model, discharge tube, Rutherford experiment, acid rain formation).
· Focus on key terms and examples – they are important for marks.
· Avoid excluded topics – these notes contain only ALP 2025–26 included content.
Best of luck for your final exams! 🧪📚
