These essential MCQ questions are selected from the most important topics in CBSE Class 10 Science 2026 as per the latest NCERT syllabus. Sections include Life Processes, Control & Coordination, Electricity, Magnetic Effects of Current, Light — Reflection & Refraction, Carbon & its Compounds, Heredity & Evolution, and Our Environment. For truly unlimited daily MCQ practice, visit Vooo AI Education.
🔬 CBSE Class 10 Science
1Which blood vessel carries oxygenated blood from the lungs to the heart?
Answer: B — Pulmonary vein
The pulmonary vein is unique — it is the only vein that carries oxygenated blood (from lungs to the left atrium of the heart). All other veins carry deoxygenated blood. The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs. The aorta carries oxygenated blood from the left ventricle to the body. Vena cava (superior and inferior) carries deoxygenated blood from the body to the right atrium.
The pulmonary vein is unique — it is the only vein that carries oxygenated blood (from lungs to the left atrium of the heart). All other veins carry deoxygenated blood. The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs. The aorta carries oxygenated blood from the left ventricle to the body. Vena cava (superior and inferior) carries deoxygenated blood from the body to the right atrium.
2Ohm's Law states that current through a conductor is:
Answer: B — Directly proportional to voltage
Ohm's Law: V = IR, where V is voltage (volts), I is current (amperes), and R is resistance (ohms). At constant temperature, V ∝ I, so current is directly proportional to voltage. Resistance (R = V/I) is the constant of proportionality. Doubling the voltage doubles the current. Conductors that obey Ohm's Law are called ohmic conductors (e.g., metals at constant temperature). Semiconductors and diodes are non-ohmic (don't obey Ohm's Law).
Ohm's Law: V = IR, where V is voltage (volts), I is current (amperes), and R is resistance (ohms). At constant temperature, V ∝ I, so current is directly proportional to voltage. Resistance (R = V/I) is the constant of proportionality. Doubling the voltage doubles the current. Conductors that obey Ohm's Law are called ohmic conductors (e.g., metals at constant temperature). Semiconductors and diodes are non-ohmic (don't obey Ohm's Law).
3When light travels from a denser medium to a rarer medium, it:
Answer: B — Bends away from the normal
Refraction of light: when light goes from denser (glass/water) to rarer medium (air), it bends away from the normal (angle of refraction > angle of incidence). When light goes from rarer to denser, it bends towards the normal. The refractive index n = sin i / sin r (Snell's Law). A convex lens (converging) has higher refractive index than air. This principle explains why objects in water appear shallower than they actually are.
Refraction of light: when light goes from denser (glass/water) to rarer medium (air), it bends away from the normal (angle of refraction > angle of incidence). When light goes from rarer to denser, it bends towards the normal. The refractive index n = sin i / sin r (Snell's Law). A convex lens (converging) has higher refractive index than air. This principle explains why objects in water appear shallower than they actually are.
4The functional unit of kidney responsible for filtration of blood is:
Answer: C — Nephron
The nephron is the structural and functional unit of the kidney. Each kidney contains about one million nephrons. A nephron consists of the glomerulus (a capillary network for filtration), Bowman's capsule, and a renal tubule for reabsorption and secretion. The final product is urine. Neuron is the functional unit of the nervous system. Alveolus is the functional unit of the lungs. Villus is found in the small intestine for absorption of nutrients.
The nephron is the structural and functional unit of the kidney. Each kidney contains about one million nephrons. A nephron consists of the glomerulus (a capillary network for filtration), Bowman's capsule, and a renal tubule for reabsorption and secretion. The final product is urine. Neuron is the functional unit of the nervous system. Alveolus is the functional unit of the lungs. Villus is found in the small intestine for absorption of nutrients.
5The homologous series of carbon compounds with general formula CₙH₂ₙ₊₁OH are called:
Answer: C — Alcohols
Alcohols have the functional group –OH (hydroxyl) and general formula CₙH₂ₙ₊₁OH. Examples: methanol (CH₃OH), ethanol (C₂H₅OH). Alkanes: CₙH₂ₙ₊₂ (no functional group). Carboxylic acids: –COOH group, formula CₙH₂ₙ₊₁COOH (e.g., acetic acid CH₃COOH). Aldehydes: –CHO group. In Class 10, ethanol (ethyl alcohol — found in alcoholic drinks) and ethanoic acid (acetic acid — vinegar) are key examples of carbon compounds with functional groups.
Alcohols have the functional group –OH (hydroxyl) and general formula CₙH₂ₙ₊₁OH. Examples: methanol (CH₃OH), ethanol (C₂H₅OH). Alkanes: CₙH₂ₙ₊₂ (no functional group). Carboxylic acids: –COOH group, formula CₙH₂ₙ₊₁COOH (e.g., acetic acid CH₃COOH). Aldehydes: –CHO group. In Class 10, ethanol (ethyl alcohol — found in alcoholic drinks) and ethanoic acid (acetic acid — vinegar) are key examples of carbon compounds with functional groups.
6Mendel's law of segregation states that two alleles for each trait:
Answer: B — Separate during gamete formation
Mendel's Law of Segregation (Law of Purity of Gametes): the two alleles of a gene pair in an organism separate (segregate) during meiosis so that each gamete receives only one allele. Example: in a Tt (tall) plant, gametes are T or t (not Tt). When two Tt plants cross, the offspring ratio is 3 tall : 1 short (3:1). Dominant alleles mask recessive ones. This law was demonstrated using pea plants (Pisum sativum) with 7 contrasting traits.
Mendel's Law of Segregation (Law of Purity of Gametes): the two alleles of a gene pair in an organism separate (segregate) during meiosis so that each gamete receives only one allele. Example: in a Tt (tall) plant, gametes are T or t (not Tt). When two Tt plants cross, the offspring ratio is 3 tall : 1 short (3:1). Dominant alleles mask recessive ones. This law was demonstrated using pea plants (Pisum sativum) with 7 contrasting traits.
7Which of the following is a non-renewable source of energy?
Answer: C — Coal
Non-renewable energy sources are formed over millions of years and cannot be replenished quickly — coal, petroleum, and natural gas (fossil fuels) and nuclear fuels. Renewable sources can be replenished naturally — solar, wind, hydro, tidal, geothermal, and biomass energy. Coal releases CO₂ when burned, contributing to the greenhouse effect. India is working to increase its renewable energy share significantly. The Sun is the ultimate source of most energy on Earth (except nuclear and geothermal).
Non-renewable energy sources are formed over millions of years and cannot be replenished quickly — coal, petroleum, and natural gas (fossil fuels) and nuclear fuels. Renewable sources can be replenished naturally — solar, wind, hydro, tidal, geothermal, and biomass energy. Coal releases CO₂ when burned, contributing to the greenhouse effect. India is working to increase its renewable energy share significantly. The Sun is the ultimate source of most energy on Earth (except nuclear and geothermal).
8Two resistors of 3Ω and 6Ω are connected in parallel. The equivalent resistance is:
Answer: C — 2Ω
For parallel resistors: 1/R = 1/R₁ + 1/R₂ = 1/3 + 1/6 = 2/6 + 1/6 = 3/6 = 1/2. So R = 2Ω. In parallel, equivalent resistance is always less than the smallest individual resistance. For series: R = R₁ + R₂ = 3 + 6 = 9Ω. In homes, appliances are connected in parallel so each gets full voltage and can be switched independently. The current splits in parallel; voltage is the same across all parallel branches.
For parallel resistors: 1/R = 1/R₁ + 1/R₂ = 1/3 + 1/6 = 2/6 + 1/6 = 3/6 = 1/2. So R = 2Ω. In parallel, equivalent resistance is always less than the smallest individual resistance. For series: R = R₁ + R₂ = 3 + 6 = 9Ω. In homes, appliances are connected in parallel so each gets full voltage and can be switched independently. The current splits in parallel; voltage is the same across all parallel branches.
9The process of conversion of glucose to ethanol by yeast in the absence of oxygen is called:
Answer: C — Anaerobic respiration
Anaerobic respiration (fermentation) occurs without oxygen: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + energy (less ATP). Yeast produces ethanol and CO₂. In our muscles during intense exercise, anaerobic respiration produces lactic acid causing muscle cramps. Aerobic respiration (with oxygen): C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 38 ATP (much more energy). Fermentation is used in making bread (CO₂ makes dough rise), wine, beer, and idli/dosa batter.
Anaerobic respiration (fermentation) occurs without oxygen: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + energy (less ATP). Yeast produces ethanol and CO₂. In our muscles during intense exercise, anaerobic respiration produces lactic acid causing muscle cramps. Aerobic respiration (with oxygen): C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 38 ATP (much more energy). Fermentation is used in making bread (CO₂ makes dough rise), wine, beer, and idli/dosa batter.
10Which layer of the atmosphere contains the ozone layer?
Answer: B — Stratosphere
The ozone layer is located in the stratosphere, approximately 15–35 km above Earth's surface. It absorbs harmful UV-B radiation from the Sun, protecting life on Earth. The troposphere (0–12 km) is where weather occurs and where we live. The mesosphere (50–80 km) burns up meteors. The thermosphere contains the ionosphere where auroras occur. CFCs (chlorofluorocarbons) from refrigerants and aerosols destroy ozone molecules, causing the ozone hole, largest over Antarctica.
The ozone layer is located in the stratosphere, approximately 15–35 km above Earth's surface. It absorbs harmful UV-B radiation from the Sun, protecting life on Earth. The troposphere (0–12 km) is where weather occurs and where we live. The mesosphere (50–80 km) burns up meteors. The thermosphere contains the ionosphere where auroras occur. CFCs (chlorofluorocarbons) from refrigerants and aerosols destroy ozone molecules, causing the ozone hole, largest over Antarctica.
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