CBSE Class 10 Science (2025-26)

Cheatsheet Content

Chemical Reactions & Equations Chemical Equation: Symbolic representation of a chemical reaction. Reactants on LHS, products on RHS. Balanced equation: Atoms of each element equal on both sides (Law of Conservation of Mass). Types of Reactions: Combination: $A + B \rightarrow AB$ (e.g., $CaO + H_2O \rightarrow Ca(OH)_2$) Decomposition: $AB \rightarrow A + B$ (e.g., $CaCO_3 \rightarrow CaO + CO_2$) Thermal, Electrolytic, Photolytic Displacement: $A + BC \rightarrow AC + B$ (More reactive element displaces less reactive) Double Displacement: $AB + CD \rightarrow AD + CB$ (Exchange of ions, often forms precipitate) Redox: Oxidation (gain of oxygen/loss of hydrogen/loss of electrons), Reduction (loss of oxygen/gain of hydrogen/gain of electrons) Corrosion: Metals react with air/moisture (e.g., rusting of iron). Rancidity: Oxidation of fats and oils in food, causing bad smell/taste. Prevented by antioxidants, N2 packaging, refrigeration. Acids, Bases & Salts Acids: Sour taste, turn blue litmus red, produce $H^+$ ions in water. (e.g., $HCl, H_2SO_4$) Bases: Bitter taste, turn red litmus blue, produce $OH^-$ ions in water. (e.g., $NaOH, Ca(OH)_2$) pH Scale: Measures $H^+$ ion concentration. $0-7$ (acidic), $7$ (neutral), $7-14$ (basic). $pH = -\log[H^+]$ Neutralisation Reaction: Acid + Base $\rightarrow$ Salt + Water (e.g., $HCl + NaOH \rightarrow NaCl + H_2O$) Important Salts: Common Salt ($NaCl$): Raw material for $NaOH$, bleaching powder, baking soda, washing soda. Bleaching Powder ($CaOCl_2$): For bleaching cotton, disinfectant. Baking Soda ($NaHCO_3$): Antacid, baking, fire extinguishers. Washing Soda ($Na_2CO_3 \cdot 10H_2O$): Cleaning agent, softening hard water. Plaster of Paris ($CaSO_4 \cdot \frac{1}{2}H_2O$): For fractures, decorative purposes. Metals & Non-metals Physical Properties: Metals: Lustrous, malleable, ductile, sonorous, good conductors of heat & electricity, high melting/boiling points. (Exception: Hg liquid, Na/K soft) Non-metals: Dull, brittle, non-sonorous, poor conductors (Exception: Graphite conductive), low melting/boiling points. Chemical Properties: Reaction with Air: Metals form metal oxides (basic). Non-metals form non-metal oxides (acidic). Amphoteric oxides (e.g., $Al_2O_3, ZnO$) react with both acids and bases. Reaction with Water: Metals react with water to form metal hydroxide/oxide + hydrogen. (Reactivity series important) Reaction with Acids: Metals react with dilute acids to form salt + hydrogen. Reactivity Series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au Ionic Bonds: Formed by transfer of electrons (metal + non-metal). High melting/boiling point, soluble in water, conduct electricity in molten/aqueous state. Covalent Bonds: Formed by sharing of electrons (non-metal + non-metal). Low melting/boiling point, generally insoluble, do not conduct electricity. Extraction of Metals: High Reactivity: Electrolysis of molten ore. Medium Reactivity: Roasting (sulfide ores) or Calcination (carbonate ores) $\rightarrow$ Reduction. Low Reactivity: Heating alone (e.g., HgS). Carbon & Its Compounds Carbon: Tetravalency, Catenation (self-linking property). Allotropes of Carbon: Diamond (hardest substance, insulator), Graphite (soft, conductor), Fullerene. Hydrocarbons: Saturated: Alkanes (single bonds, CnH2n+2). Unsaturated: Alkenes (double bonds, CnH2n), Alkynes (triple bonds, CnH2n-2). Functional Groups: Alcohol (-OH), Aldehyde (-CHO), Ketone (C=O), Carboxylic Acid (-COOH), Haloalkanes (-X). Homologous Series: Similar chemical properties, differ by $-CH_2$ group. Chemical Properties of Carbon Compounds: Combustion: Hydrocarbon + O2 $\rightarrow$ CO2 + H2O + Heat + Light. Oxidation: Alcohols to carboxylic acids (using KMnO4/K2Cr2O7). Addition Reaction: Unsaturated hydrocarbons to saturated (hydrogenation, using Ni/Pd catalyst). Substitution Reaction: Saturated hydrocarbons react with halogens in presence of sunlight. Ethanol ($C_2H_5OH$): Alcohol, solvent, fuel. Ethanoic Acid ($CH_3COOH$): Carboxylic acid, vinegar (5-8% solution). Esterification with alcohol. Soaps & Detergents: Soaps: Sodium/potassium salts of long-chain fatty acids. Form scum with hard water. Detergents: Long-chain alkyl benzene sulphonates. Work well in hard water. Micelle Formation: Hydrophobic tail and hydrophilic head. Traps dirt. Periodic Classification of Elements Early Attempts: Dobereiner's Triads, Newlands' Law of Octaves. Mendeleev's Periodic Table: Based on atomic mass. Left gaps for undiscovered elements. Modern Periodic Table: Based on atomic number (Moseley). Periods (horizontal rows): Number of shells. Groups (vertical columns): Number of valence electrons, similar chemical properties. Metals on left, non-metals on right, metalloids along zig-zag line. Periodic Trends: Valency: First increases, then decreases across a period. Constant in a group. Atomic Size: Decreases across a period (due to increased nuclear charge). Increases down a group (new shells added). Metallic Character: Decreases across a period. Increases down a group. Non-metallic Character: Increases across a period. Decreases down a group. Life Processes Nutrition: Autotrophic: Plants (photosynthesis: $6CO_2 + 6H_2O \xrightarrow{sunlight, chlorophyll} C_6H_{12}O_6 + 6O_2$). Heterotrophic: Animals (holozoic, saprophytic, parasitic). Human Digestive System: Mouth $\rightarrow$ Esophagus $\rightarrow$ Stomach $\rightarrow$ Small Intestine $\rightarrow$ Large Intestine. Enzymes: Amylase (starch), Pepsin/Trypsin (proteins), Lipase (fats). Villi in small intestine increase surface area for absorption. Respiration: Aerobic: Glucose + O2 $\rightarrow$ CO2 + H2O + Energy (in mitochondria). Anaerobic: Glucose $\rightarrow$ Ethanol + CO2 + Energy (yeast) or Lactic Acid + Energy (muscle cells). Human Respiratory System: Nasal passage $\rightarrow$ Pharynx $\rightarrow$ Larynx $\rightarrow$ Trachea $\rightarrow$ Bronchi $\rightarrow$ Bronchioles $\rightarrow$ Alveoli (gas exchange). Transportation: Plants: Xylem (water, minerals - unidirectional), Phloem (food - bidirectional). Transpiration pull. Human Circulatory System: Heart (4 chambers), Blood (RBC, WBC, platelets, plasma), Blood Vessels (arteries, veins, capillaries). Double Circulation: Pulmonary (heart-lungs) and Systemic (heart-body). Excretion: Plants: Gaseous waste (stomata), stored waste (leaves, bark, gums, resins). Human Excretory System: Kidneys (filter blood), Ureters, Urinary Bladder, Urethra. Nephron: Functional unit of kidney (filtration, reabsorption, secretion). Control & Coordination Animals: Nervous System: Brain, Spinal Cord, Nerves. Neuron: Structural & functional unit. Dendrite $\rightarrow$ Cell Body $\rightarrow$ Axon $\rightarrow$ Nerve Ending. Synapse: Junction between two neurons. Neurotransmitters. Reflex Arc: Stimulus $\rightarrow$ Receptor $\rightarrow$ Sensory Neuron $\rightarrow$ Spinal Cord $\rightarrow$ Motor Neuron $\rightarrow$ Effector $\rightarrow$ Response. Brain: Forebrain (cerebrum - thought, memory), Midbrain, Hindbrain (cerebellum - balance, medulla - involuntary actions). Endocrine System: Hormones (chemical messengers). Pituitary (growth), Thyroid (metabolism), Adrenal (fight or flight), Pancreas (insulin/glucagon - blood sugar), Testes (testosterone), Ovaries (estrogen). Plants: Plant Hormones (Phytohormones): Auxins (growth, phototropism, geotropism), Gibberellins (stem growth), Cytokinins (cell division), Abscisic Acid (inhibitor, dormancy), Ethylene (fruit ripening). Tropisms: Directional growth in response to stimuli. Phototropism (light), Geotropism (gravity), Hydrotropism (water), Chemotropism (chemicals). How Do Organisms Reproduce? Reproduction: Creation of new organisms. Ensures continuity of life. Asexual Reproduction: Single parent, no gamete fusion, genetically identical offspring. Fission (binary - amoeba, multiple - plasmodium), Fragmentation (spirogyra), Regeneration (planaria), Budding (hydra, yeast), Spore Formation (rhizopus), Vegetative Propagation (plants - cutting, layering, grafting). Sexual Reproduction: Two parents, gamete fusion, genetic variation. Flowering Plants: Flower (sepals, petals, stamens - male, carpels - female). Pollination (self, cross), Fertilization (fusion of male & female gametes). Zygote $\rightarrow$ Embryo. Ovary $\rightarrow$ Fruit, Ovule $\rightarrow$ Seed. Human Reproductive System: Male: Testes (sperm, testosterone), Vas deferens, Urethra, Penis. Female: Ovaries (eggs, estrogen, progesterone), Oviducts (fallopian tubes - fertilization), Uterus (implantation, development), Vagina. Menstrual Cycle: Monthly cycle in females, prepares uterus for pregnancy. Reproductive Health: STDs, Contraception (barrier, oral pills, IUDs, surgical methods). Heredity & Evolution Heredity: Transmission of traits from parents to offspring. Variation: Differences among individuals of a species. Important for evolution. Mendel's Laws: Law of Dominance: In a cross, only dominant trait expresses. Law of Segregation: Alleles separate during gamete formation. Law of Independent Assortment: Genes for different traits assort independently. Genotype: Genetic makeup (e.g., TT, Tt). Phenotype: Observable trait (e.g., Tall, Dwarf). Sex Determination: In humans, XX (female), XY (male). Father determines sex of child. Evolution: Gradual change in living organisms over generations. Acquired Traits: Developed during lifetime, not inherited (e.g., learning to read). Inherited Traits: Passed from parents, genetic (e.g., eye color). Evidence of Evolution: Homologous organs (same structure, different function), Analogous organs (different structure, same function), Fossils. Speciation: Formation of new species due to genetic drift, natural selection, geographical isolation. Light - Reflection & Refraction Reflection: Bouncing back of light. Law of Reflection: Angle of incidence = Angle of reflection; Incident ray, reflected ray, normal lie in same plane. Plane Mirror: Virtual, erect, same size, same distance behind mirror. Spherical Mirrors: Concave (converging), Convex (diverging). Mirror Formula: $\frac{1}{f} = \frac{1}{v} + \frac{1}{u}$ (focal length, image distance, object distance). Magnification: $m = \frac{h'}{h} = -\frac{v}{u}$. Sign Convention: Distances measured from pole. Real is positive, virtual is negative. Upward is positive, downward is negative. Refraction: Bending of light as it passes from one medium to another. Cause: Change in speed of light. Snell's Law: $\frac{\sin i}{\sin r} = n$ (refractive index). Lenses: Convex (converging), Concave (diverging). Lens Formula: $\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$. Magnification: $m = \frac{h'}{h} = \frac{v}{u}$. Power of Lens: $P = \frac{1}{f}$ (in meters), unit Dioptre (D). Human Eye & Colourful World Human Eye: Cornea, Iris, Pupil, Ciliary Muscles, Lens, Retina, Optic Nerve. Accommodation: Ability of eye lens to adjust focal length. Persistence of Vision: Image stays for $1/16$ second. Defects of Vision: Myopia (Nearsightedness): Distant objects unclear. Corrected by concave lens. Hypermetropia (Farsightedness): Near objects unclear. Corrected by convex lens. Presbyopia: Due to aging, loss of accommodation. Corrected by bifocal lens. Dispersion of Light: Splitting of white light into constituent colours (VIBGYOR). Caused by different refractive indices for different colours. Atmospheric Refraction: Twinkling of stars, advance sunrise and delayed sunset. Scattering of Light: Tyndall effect, Blue sky, Reddish sunrise/sunset (due to scattering of shorter wavelengths). Electricity Electric Current (I): Rate of flow of charge. $I = \frac{Q}{t}$, unit Ampere (A). $Q=ne$. Electric Potential Difference (V): Work done per unit charge. $V = \frac{W}{Q}$, unit Volt (V). Ohm's Law: $V = IR$ (Voltage, Current, Resistance), unit Ohm ($\Omega$). Resistance: Obstruction to current flow. $R = \rho \frac{L}{A}$ ($\rho$ = resistivity, L = length, A = area). Resistors in Series: $R_{eq} = R_1 + R_2 + ...$ (Current same, voltage divides). Resistors in Parallel: $\frac{1}{R_{eq}} = \frac{1}{R_1} + \frac{1}{R_2} + ...$ (Voltage same, current divides). Heating Effect of Current (Joule's Law): $H = I^2Rt = VIt = \frac{V^2}{R}t$. Applications: electric heater, bulb. Electric Power (P): Rate of doing work. $P = VI = I^2R = \frac{V^2}{R}$, unit Watt (W). Commercial unit of energy: kilowatt-hour (kWh). $1 kWh = 3.6 \times 10^6 J$. Magnetic Effects of Electric Current Magnetic Field: Region around a magnet where its force is felt. Field lines originate from N-pole, end at S-pole, never intersect. Magnetic Field due to Current: Straight Conductor: Concentric circles (Right Hand Thumb Rule). Circular Loop: Field lines form loops, stronger at center. Solenoid: Behaves like a bar magnet. Field inside is uniform and strong. Force on a Current-Carrying Conductor: $F = BIL\sin\theta$. Direction by Fleming's Left Hand Rule (Thumb-Force, Forefinger-Field, Middle finger-Current). Applications: Electric motor, galvanometer. Electromagnetic Induction (EMI): Production of induced current due to change in magnetic field. Direction by Fleming's Right Hand Rule (Thumb-Motion, Forefinger-Field, Middle finger-Induced Current). Applications: Electric generator, transformer. Electric Motor: Converts electrical energy to mechanical energy. Principle: Force on current-carrying conductor in magnetic field. Electric Generator: Converts mechanical energy to electrical energy. Principle: EMI. AC Generator: Produces alternating current. DC Generator: Produces direct current (using split-ring commutator). Domestic Electric Circuits: Live wire (red), Neutral wire (black), Earth wire (green). Short circuiting, overloading, fuses. Sources of Energy Good Source of Energy: Easily accessible, safe, efficient, economical. Conventional Sources: Fossil Fuels: Coal, petroleum, natural gas. Non-renewable, cause pollution. Thermal Power Plant: Burns fossil fuels to produce steam, drives turbines. Hydro Power Plant: Converts potential energy of water to kinetic, drives turbines. Renewable, but environmental issues. Biomass: Plant/animal waste. Biogas plant. Wind Energy: Wind turbines. Renewable, but needs consistent wind. Non-Conventional Sources: Solar Energy: Solar panels (photovoltaic cells), solar cookers. Ocean Thermal Energy Conversion (OTEC): Uses temperature difference in ocean. Geothermal Energy: Heat from Earth's interior. Nuclear Energy: Nuclear fission (U-235). High energy, but radioactive waste disposal issue. Environmental Consequences: Burning fossil fuels causes air pollution, acid rain, greenhouse effect, global warming. Conservation of Energy: Reduce, Reuse, Recycle. Our Environment Ecosystem: All living organisms (biotic) and non-living components (abiotic) in an area. Components: Producers (autotrophs), Consumers (heterotrophs), Decomposers (bacteria, fungi). Food Chain: Transfer of energy from one organism to another (e.g., Grass $\rightarrow$ Deer $\rightarrow$ Tiger). Food Web: Interconnected food chains. Trophic Levels: Producers (1st), Primary Consumers (2nd), Secondary Consumers (3rd), Tertiary Consumers (4th). 10% Law: Only 10% of energy is transferred from one trophic level to the next. Biological Magnification: Accumulation of non-biodegradable chemicals (e.g., DDT) in increasing concentrations at successive trophic levels. Ozone Layer ($O_3$): Protects Earth from harmful UV radiation. Depleted by CFCs (chlorofluorocarbons). Waste Management: Biodegradable (decompose naturally) vs. Non-biodegradable (don't decompose). Reduce, Reuse, Recycle, Composting. Management of Natural Resources Natural Resources: Resources obtained from nature (forests, wildlife, water, coal, petroleum). Sustainable Management: Using resources wisely to meet current needs without compromising future generations. Forests & Wildlife: Conserve biodiversity, prevent deforestation, afforestation. Stakeholders (local people, forest department, industrialists, wildlife enthusiasts). Water Resources: Rainwater harvesting, check dams, traditional methods (e.g., Khadins). Pollution of rivers. Coal & Petroleum: Fossil fuels, limited stock. Use judiciously, explore alternatives. The 3 R's: Reduce, Reuse, Recycle.