CBSE Class 10 Science Important Question answers for 2025

1 Mark Questions – Short Answers

1. Which gas is evolved when a metal reacts with an acid?→ Hydrogen gas (H₂) is evolved when a metal reacts with an acid.Example:

   Zn+2HCl→ZnCl2+H2↑Zn + 2HCl → ZnCl₂ + H₂↑Zn+2HCl→ZnCl2​+H2​↑

2. Write the chemical formula of baking soda.→ The chemical formula of baking soda is NaHCO₃ (Sodium Bicarbonate).

3. What is the SI unit of power of a lens?→ The SI unit of the power of a lens is Dioptre (D). It is given by:

   P=1f(f in meters)P = \frac{1}{f} \quad (f \text{ in meters})P=f1​(f in meters)

4. State the role of the placenta in human reproduction.→ The placenta is an organ that connects the developing fetus to the uterine wall. It allows the exchange of nutrients, oxygen, and waste between the mother and the fetus through the umbilical cord.

5. Why does a ray of light bend when it passes from air to glass?→ Light bends due to refraction, which occurs because light travels slower in glass than in air, causing it to change direction.

2 Mark Questions – Brief Explanations

1. Differentiate between a convex lens and a concave lens with a ray diagram.

   FeatureConvex LensConcave LensShapeBulges outwardCurves inwardNatureConvergingDivergingImage FormedReal & inverted (except when object is between F and O)Virtual & upright

   Ray Diagram:

   • Convex Lens:

     
     

   • Concave Lens:

     

     Ray Diagram- Image by Byju'https://byjus.com/physics/concave-convex-lenses/s

2. State Newton’s third law of motion and give one example.

   
   

   → Newton’s Third Law: For every action, there is an equal and opposite reaction.

   
   

   Example: When a person jumps from a boat, the boat moves backward as the person moves forward.

3. Why is the color of the sky blue?

   
   

   → The sky appears blue due to Rayleigh scattering. Shorter-wavelength blue light is scattered more than longer-wavelength red light by the Earth's atmosphere.

   
   

4. Write the balanced chemical equation for the reaction between sodium hydroxide and hydrochloric acid. NaOH+HCl→NaCl+H2ONaOH + HCl → NaCl + H₂ONaOH+HCl→NaCl+H2​O This reaction is called neutralization, producing salt (NaCl) and water (H₂O).

   
   

5. List two advantages of vegetative propagation in plants.

   • Faster growth: New plants grow quickly without seeds.

   • Exact copies: Offspring are genetically identical to the parent, maintaining desirable traits.

3 Mark Questions – Detailed Explanations

1. Explain the mechanism of the cleaning action of soap with a labeled diagram.

   Mechanism:

   • Soap molecules have a hydrophobic tail (repels water) and a hydrophilic head (attracts water).

   • Dirt and oil dissolve in the hydrophobic tail, while water washes away the hydrophilic head, forming micelles.

   Diagram:

   

   Mechanism of the cleaning action of soap with a labeled diagram.

   
   

2. Describe the structure of the human heart with a neat diagram.

   Structure:

   • The heart is a muscular organ with four chambers:

     • Right atrium & right ventricle (carry deoxygenated blood)

     • Left atrium & left ventricle (carry oxygenated blood)

   • Blood circulation is controlled by valves (mitral, tricuspid, pulmonary, aortic).

   Diagram:

   

   Structure of the human heart

   
   

3. Why do ionic compounds have high melting points? Explain with an example.

   • Ionic compounds have strong electrostatic forces between positively and negatively charged ions, requiring a lot of energy to break these bonds.

   • Example: Sodium chloride (NaCl) has a high melting point due to strong Na⁺ and Cl⁻ attractions.

5 Mark Questions – Long Answers

1. Explain the process of digestion in humans with a labeled diagram.

   Process:

   • Mouth: Saliva breaks down starch.

   • Stomach: HCl and enzymes break proteins.

   • Small Intestine: Pancreatic enzymes digest carbohydrates, proteins, and fats.

   • Large Intestine: Absorbs water and excretes waste.

   Diagram:

   

   digestion in humans with a labeled diagram

   
   

2. Describe the electrolysis of water and write the chemical equations involved.

   Electrolysis Process:

   • Water (H₂O) is decomposed into hydrogen (H₂) and oxygen (O₂) gases by passing electricity through it.

   • At cathode (-): 2H++2e−→H2↑2H⁺ + 2e⁻ → H₂↑2H++2e−→H2​↑

   • At anode (+): 4OH−→O2+2H2O+4e−4OH⁻ → O₂ + 2H₂O + 4e⁻4OH−→O2​+2H2​O+4e−

3. Explain Mendel’s experiment on pea plants and state the laws of inheritance.

   Mendel’s Experiment:

   • He crossed tall (TT) and dwarf (tt) pea plants.

   • In F₁ Generation, all plants were tall (Tt).

   • In F₂ Generation, 3 tall:1 dwarf ratio appeared.

   Laws of Inheritance:

   1. Law of Dominance – Dominant traits appear in F₁.

   2. Law of Segregation – Alleles separate during gamete formation.

   3. Law of Independent Assortment – Genes for different traits inherit independently.

4. What is the magnetic effect of electric current? Explain with Oersted’s experiment and the right-hand thumb rule.

   Magnetic Effect of Current:

   • When electric current flows through a conductor, it creates a magnetic field around it.

   Oersted’s Experiment:

   • A compass needle deflected when placed near a current-carrying wire, proving electric current produces magnetism.

   Right-Hand Thumb Rule:

   • If you point your thumb in the direction of current, the curled fingers show the direction of the magnetic field.

5. Draw a labeled diagram of the female reproductive system and explain the process of fertilization.

   Fertilization Process:

   • The sperm meets the egg in the fallopian tube.

   • The zygote forms and implants in the uterus.

   Diagram:

   

   Female reproductive system

SET 2 CBSE Class 10 Science Important Question Answers for 2025

1 Mark Questions – Short Answers

1. What is the chemical formula of hydrochloric acid?→ The chemical formula of hydrochloric acid is HCl.

2. Which gas is released when zinc reacts with dilute sulfuric acid?→ The gas released is Hydrogen (H₂).Chemical equation:

   Zn+H2SO4→ZnSO4+H2↑Zn + H_2SO_4 \rightarrow ZnSO_4 + H_2↑Zn+H2​SO4​→ZnSO4​+H2​↑

3. What is the SI unit of electric current?→ The SI unit of electric current is the Ampere (A).

4. What is meant by ‘latent heat of fusion’?→ Latent heat of fusion is the amount of heat required to change 1 kg of a solid into a liquid at its melting point, without changing its temperature.

5. What is the main function of the xylem in plants?→ The main function of xylem is to transport water and minerals from the roots to the leaves and other parts of the plant.

2 Mark Questions – Brief Explanations

1. What is the difference between reflection and refraction?

   • Reflection is the bouncing back of light when it hits a surface.

   • Refraction is the bending of light as it passes from one medium to another.

2. What are the different types of lenses? Explain briefly.

   • Convex Lens: It is thicker at the center than at the edges. It converges light rays.

   • Concave Lens: It is thinner at the center than at the edges. It diverges light rays.

3. What are the three main components of a plant cell?The three main components are:

   1. Cell wall (provides structure and support)

   2. Chloroplasts (involved in photosynthesis)

   3. Nucleus (controls the cell’s activities)

4. What is the significance of the ozone layer?The ozone layer absorbs most of the Sun’s harmful ultraviolet (UV) radiation, protecting living organisms from the detrimental effects of UV rays.

5. Explain the process of transpiration in plants.Transpiration is the loss of water vapor from the aerial parts of plants, especially from the stomata. It helps in the uptake of minerals and water from the roots and also cools the plant.

3 Mark Questions – Detailed Explanations

1. Explain the process of photosynthesis with a chemical equation.Photosynthesis is the process by which plants prepare their food using carbon dioxide, water, and sunlight.Chemical Equation:

   6CO2+6H2O+light energy→C6H12O6+6O26CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_26CO2​+6H2​O+light energy→C6​H12​O6​+6O2​

   This process takes place in the chloroplasts in the presence of chlorophyll.

2. Describe the process of breathing in humans.Breathing involves inhalation and exhalation:

   • During inhalation, air enters the lungs, and oxygen from the air is absorbed into the blood.

   • During exhalation, carbon dioxide is expelled from the body. The process is controlled by the diaphragm and intercostal muscles.

3. What is the difference between asexual and sexual reproduction in plants?

   • Asexual Reproduction: Involves only one parent and results in genetically identical offspring (e.g., vegetative propagation).

   • Sexual Reproduction: Involves two parents and produces genetically diverse offspring through the fusion of male and female gametes (e.g., fertilization in flowers).

4. Explain the concept of the law of conservation of mass with an example.The law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction. The total mass of reactants equals the total mass of products.Example: When carbon burns in oxygen to form carbon dioxide:

   C+O2→CO2C + O_2 → CO_2C+O2​→CO2​

   The mass of carbon and oxygen before the reaction equals the mass of the carbon dioxide produced.

5. What is the role of the digestive system in humans? Explain with a diagram.The digestive system helps in the breakdown of food into simpler forms that can be absorbed by the body.Main Organs Involved:

   • Mouth: Breaks down food mechanically and chemically.

   • Esophagus: Transports food to the stomach.

   • Stomach: Continues digestion with acid and enzymes.

   • Small intestine: Completes digestion and absorbs nutrients.

   • Large intestine: Absorbs water and forms solid waste.

   
   
   
   

5 Mark Questions – Long Answers

1. Explain the structure of an atom with a labeled diagram.

   • An atom consists of three basic subatomic particles:

     • Protons (p⁺): Positive charge, located in the nucleus.

     • Neutrons (n°): No charge, also in the nucleus.

     • Electrons (e⁻): Negative charge, revolve around the nucleus in energy levels or shells.

       
       

2. What is the role of the Sun in the water cycle? Explain.The Sun plays a critical role in the water cycle by providing energy for evaporation of water from oceans, lakes, and rivers.

   • The evaporated water then condenses to form clouds, and eventually falls back to Earth as precipitation (rain, snow, etc.).

   • The cycle repeats as the water is again evaporated by the Sun’s heat.

3. What is electromagnetic induction? Explain Faraday’s law of induction.

   • Electromagnetic induction is the process of generating an electric current by changing the magnetic field.

   • Faraday’s Law states that the induced electromotive force (EMF) is directly proportional to the rate of change of the magnetic flux linked with a coil.

   E=−dΦBdt\mathcal{E} = -\frac{d\Phi_B}{dt}E=−dtdΦB​​

   Where Φ_B is the magnetic flux and dΦ_B/dt is the rate of change of flux.

4. Explain the structure and function of DNA.

   • DNA (Deoxyribonucleic Acid) is a double-stranded molecule that carries genetic information.

   • It consists of nucleotides, each containing a sugar, phosphate group, and a nitrogenous base (A, T, C, G).

   • The DNA molecule forms a double helix structure and stores instructions for building proteins.

   • Function: DNA is responsible for inheritance and controlling cell functions.

5. Explain how the force between two electric charges is calculated.

   • The force between two electric charges is given by Coulomb’s Law:

   F=kq1q2r2F = k \frac{q_1 q_2}{r^2}F=kr2q1​q2​​

   Where:

   • F = force between the charges

   • q₁ and q₂ = magnitudes of the charges

   • r = distance between the charges

   • k = Coulomb’s constant (8.99 × 10⁹ N·m²/C²)