Science MCQS
Science Solved MCQs
Q1. Most abundant gas in Earth’s atmosphere ?
Ans: Nitrogen.
Explanation: Nitrogen makes up about 78% of Earth’s atmosphere. It is essential for plant growth and protein formation but is not directly used in human respiration.
Q2. Which organ pumps blood throughout the body ?
Ans: Heart.
Explanation: The heart pumps oxygenated blood through arteries and receives deoxygenated blood through veins, maintaining the continuous circulation needed for life functions.
Q3. Chemical symbol for water ?
Ans: H₂O.
Explanation: Water consists of two hydrogen atoms and one oxygen atom. It is essential for all living organisms and most biochemical reactions occur in water.
Q4. Which planet is called the “Red Planet” ?
Ans: Mars.
Explanation: Mars appears red because of iron oxide (rust) on its surface. It’s the fourth planet from the Sun and often studied for possible life.
Q5. Boiling point of water (Celsius) ?
Ans: 100°C.
Explanation: At normal atmospheric pressure, pure water boils at 100°C, changing from liquid to vapor due to heat energy breaking molecular bonds.
Q6. Which vitamin comes from sunlight ?
Ans: Vitamin D.
Explanation: The skin produces Vitamin D when exposed to sunlight. It helps the body absorb calcium, maintaining strong bones and teeth.
Q7. Unit of electric current ?
Ans: Ampere.
Explanation: The Ampere (A) measures the rate of flow of electric charge in a circuit. It represents one coulomb of charge passing per second.
Q8. Process used by plants to make food ?
Ans: Photosynthesis.
Explanation: Green plants use sunlight, carbon dioxide, and water to make glucose and oxygen. Chlorophyll in leaves absorbs sunlight to drive this process.
Q9. Hardest natural substance on Earth ?
Ans: Diamond.
Explanation: Diamond is made of carbon atoms arranged in a strong crystal lattice, giving it unmatched hardness used in jewelry and cutting tools.
Q10. Part of the cell containing genetic material ?
Ans: Nucleus.
Explanation: The nucleus controls cell activities and stores DNA, the genetic blueprint that determines inherited traits and directs protein synthesis.
Q11. Which gas do plants absorb from air ?
Ans: Carbon dioxide.
Explanation: Plants take in carbon dioxide during photosynthesis to produce glucose and release oxygen, maintaining atmospheric gas balance.
Q12. Metal liquid at room temperature ?
Ans: Mercury.
Explanation: Mercury is the only metal that remains liquid at room temperature. It is used in thermometers and electrical switches.
Q13. Main source of energy for Earth ?
Ans: Sun.
Explanation: The Sun provides light and heat energy necessary for weather, photosynthesis, and life processes on Earth.
Q14. Number of bones in adult human body ?
Ans: 206.
Explanation: An adult has 206 bones forming the skeleton, which supports the body, protects organs, and enables movement.
Q15. Organ known as the “filter” of the body ?
Ans: Kidney.
Explanation: Kidneys filter waste and excess water from blood, forming urine and maintaining body fluid balance.
Q16. What gas do humans exhale ?
Ans: Carbon dioxide.
Explanation: Humans inhale oxygen and exhale carbon dioxide as a waste product of cellular respiration in body cells.
Q17. Nearest planet to the Sun ?
Ans: Mercury.
Explanation: Mercury is the smallest and closest planet to the Sun, completing one orbit in just 88 Earth days.
Q18. Which part of the eye controls light entering ?
Ans: Pupil.
Explanation: The pupil changes size to regulate light entry — it widens in dim light and narrows in bright light.
Q19. Chemical symbol for gold ?
Ans: Au.
Explanation: “Au” comes from the Latin word “Aurum.” Gold is a yellow, non-reactive, and highly valuable metal used in jewelry and electronics.
Q20. Speed of light ?
Ans: 300,000 km/s.
Explanation: Light travels at approximately 300,000 kilometers per second in a vacuum — the fastest known speed in the universe.
Q21. pH value of pure water ?
Ans: 7.
Explanation: Pure water has a neutral pH of 7, meaning it’s neither acidic nor basic, representing equal hydrogen and hydroxide ion concentration.
Q22. Basic unit of life ?
Ans: Cell.
Explanation: The cell is the smallest structural and functional unit of life. All living organisms are made of one or more cells.
Q23. Gas humans exhale ?
Ans: Carbon dioxide.
Explanation: During respiration, body cells use oxygen to produce energy, releasing carbon dioxide as a waste gas exhaled by the lungs.
Q24. Nearest planet to the Sun ?
Ans: Mercury.
Explanation: Mercury’s close orbit to the Sun makes its surface extremely hot during the day and very cold at night.
Q25. Part of the eye controlling light entry ?
Ans: Pupil.
Explanation: The pupil acts like a camera aperture, controlling the amount of light reaching the retina for clear vision.
Q26. Chemical symbol for gold ?
Ans: Au.
Explanation: Gold’s symbol “Au” stands for “Aurum,” meaning shining dawn in Latin. It is dense, corrosion-resistant, and used in currency and ornaments.
Q27. Speed of light ?
Ans: 300,000 km/s.
Explanation: Light’s constant speed in a vacuum defines the cosmic speed limit, forming the basis for Einstein’s theory of relativity.
Q28. pH of pure water ?
Ans: 7.
Explanation: Pure water is neutral because it has equal hydrogen and hydroxide ions, making it a standard reference for measuring acidity or alkalinity.
Q29. Basic unit of life ?
Ans: Cell.
Explanation: Cells perform all vital life functions such as growth, reproduction, and metabolism, forming the foundation of all living beings.
Q30. Largest planet in our solar system ?
Ans: Jupiter.
Explanation: Jupiter is the biggest planet, mainly made of hydrogen and helium, and has a Great Red Spot — a giant storm.
Q31. Gas essential for human respiration ?
Ans: Oxygen.
Explanation: Oxygen is needed by body cells to produce energy through respiration. It’s inhaled from air and used in the mitochondria.
Q32. Which part of the plant absorbs water from soil ?
Ans: Roots.
Explanation: Plant roots absorb water and minerals from the soil through root hairs, transporting them upward to leaves for photosynthesis.