50 Best Hardest Questions in Science Class 8 with Answers

These questions are designed to test conceptual understanding and critical thinking. Answers are provided for each question.

Q: What is the SI unit of force?
A: Newton (N).
Q: Define friction. What are the types of friction?
A: Friction is the force that opposes the motion of an object. Types include static, sliding, rolling, and fluid friction.
Q: Why does a satellite in orbit not fall to Earth?
A: The satellite’s horizontal velocity balances the gravitational pull, keeping it in orbit.
Q: What is the difference between mass and weight?
A: Mass is the amount of matter in an object (measured in kg), while weight is the force exerted by gravity on that mass (measured in N).
Q: Explain the law of conservation of energy.
A: Energy cannot be created or destroyed; it can only be transformed from one form to another.
Q: What is the speed of light in a vacuum?
A: Approximately $3 \times 1 0^{8} m/s$ .
Q: Why does a balloon stick to a wall after rubbing it on hair?
A: Rubbing creates static electricity, causing the balloon to become charged and attract to the wall.
Q: What is the difference between a concave and convex lens?
A: A concave lens diverges light rays, while a convex lens converges them.
Q: What is the principle behind the working of a hydraulic lift?
A: Pascal’s law: Pressure applied to a fluid is transmitted equally in all directions.
Q: Why does sound travel faster in solids than in gases?
A: Particles in solids are closer together, allowing vibrations to transfer more quickly.

Q: What is the chemical formula of water?
A: $H_{2} O$ .
Q: Define an element and give an example.
A: An element is a pure substance made of only one type of atom (e.g., oxygen, carbon).
Q: What is the difference between a physical and chemical change?
A: A physical change alters the form of a substance without changing its composition, while a chemical change forms new substances.
Q: What is the pH of a neutral solution?
A: 7.
Q: What happens when vinegar reacts with baking soda?
A: It produces carbon dioxide gas, water, and sodium acetate.
Q: What is the atomic number of an element?
A: The number of protons in the nucleus of an atom.
Q: Why is gold used in making jewelry?
A: It is unreactive, malleable, and does not corrode.
Q: What is the chemical name of common salt?
A: Sodium chloride (NaCl).
Q: What is the process of converting a liquid into a gas called?
A: Vaporization (or evaporation).
Q: What is the difference between a compound and a mixture?
A: A compound is a pure substance formed by chemical bonding, while a mixture is a physical combination of substances.

Q: What is the function of red blood cells?
A: To transport oxygen from the lungs to the body’s tissues.
Q: Define photosynthesis. Write its equation.
A: Photosynthesis is the process by which plants make food using sunlight.
Equation: $6 C O_{2} + 6 H_{2} O light C_{6} H_{12} O_{6} + 6 O_{2}$ .
Q: What is the role of chlorophyll in plants?
A: It absorbs light energy for photosynthesis.
Q: What is the difference between aerobic and anaerobic respiration?
A: Aerobic respiration uses oxygen, while anaerobic respiration occurs without oxygen.
Q: Name the largest organ in the human body.
A: Skin.
Q: What are the three types of blood vessels?
A: Arteries, veins, and capillaries.
Q: What is the function of the nervous system?
A: To control and coordinate body activities.
Q: What is the difference between prokaryotic and eukaryotic cells?
A: Prokaryotic cells lack a nucleus and membrane-bound organelles, while eukaryotic cells have both.
Q: What is the role of white blood cells?
A: To fight infections and protect the body from diseases.
Q: What is pollination?
A: The transfer of pollen from the male part of a flower to the female part.

Q: What is the greenhouse effect?
A: The trapping of heat by greenhouse gases in the Earth’s atmosphere, leading to global warming.
Q: What are the three R’s of waste management?
A: Reduce, Reuse, Recycle.
Q: What is deforestation? How does it affect the environment?
A: Deforestation is the clearing of forests, leading to habitat loss, climate change, and soil erosion.
Q: What is the ozone layer, and why is it important?
A: A layer of ozone gas in the stratosphere that protects Earth from harmful ultraviolet (UV) radiation.
Q: What is the difference between renewable and non-renewable resources?
A: Renewable resources can be replenished (e.g., solar energy), while non-renewable resources are finite (e.g., coal).
Q: What is acid rain?
A: Rainwater with a low pH due to pollutants like sulfur dioxide and nitrogen oxides.
Q: What is the role of decomposers in an ecosystem?
A: They break down dead organic matter, recycling nutrients back into the soil.
Q: What is biodiversity?
A: The variety of life forms in an ecosystem.
Q: What is the main cause of air pollution?
A: Burning fossil fuels, industrial emissions, and vehicle exhaust.
Q: What is the importance of wetlands?
A: They filter water, provide habitat, and control floods.

Q: What is the difference between speed and velocity?
A: Speed is a scalar quantity (only magnitude), while velocity is a vector quantity (magnitude and direction).
Q: What is the formula for calculating pressure?
A: Pressure = Force / Area.
Q: What is the chemical formula of glucose?
A: $C_{6} H_{12} O_{6}$ .
Q: What is the function of the diaphragm in the human body?
A: It helps in breathing by contracting and relaxing.
Q: What is the difference between a star and a planet?
A: A star produces its own light, while a planet reflects light.
Q: What is the role of the liver in the human body?
A: It detoxifies chemicals, produces bile, and metabolizes drugs.
Q: What is the difference between a conductor and an insulator?
A: A conductor allows electricity to flow, while an insulator does not.
Q: What is the chemical formula of methane?
A: $C H_{4}$ .
Q: What is the function of the stomata in plants?
A: They allow gas exchange (oxygen and carbon dioxide) and transpiration.
Q: What is the difference between a food chain and a food web?
A: A food chain is a linear sequence of energy transfer, while a food web is a network of interconnected food chains.

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