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Total MCQs: 30Class 10 Science Chapter 1 MCQs with Answers (Online Quiz & Practice Test)
CBSE 2025–2026 Board Exam Pattern: Conceptual, Activities, Assertion-Reason & Competency Questions
💡 Online Practice Instructions: Take the interactive test using the widget above to assess your preparation. The complete answer key with detailed scientific explanations is provided below.
📖 View Complete 30 MCQs Static Answer Key & Explanations Click to Reveal / उत्तर कुंजी देखें
Complete 30 Practice MCQs & Verified Answer Key
1. In any chemical reaction, the formation of new substances involves:
(A) Breaking and making of chemical bonds
(B) Change in atomic nuclei
(C) Creation of new atoms
(D) Only changes in physical state
✅ Correct Answer: (A) Breaking and making of chemical bonds
Explanation: Chemical reactions involve the breaking of existing chemical bonds between reactant atoms and the formation of new chemical bonds to produce new products.
Explanation: Chemical reactions involve the breaking of existing chemical bonds between reactant atoms and the formation of new chemical bonds to produce new products.
2. Balancing of a chemical equation is fundamentally based on the:
(A) Law of Definite Proportions
(B) Law of Conservation of Mass
(C) Avogadro’s Law
(D) Law of Multiple Proportions
✅ Correct Answer: (B) Law of Conservation of Mass
Explanation: The Law of Conservation of Mass states that mass can neither be created nor destroyed in a chemical reaction; hence, the number of atoms of each element must remain equal on both sides.
Explanation: The Law of Conservation of Mass states that mass can neither be created nor destroyed in a chemical reaction; hence, the number of atoms of each element must remain equal on both sides.
3. In the balanced equation $3\text{Fe} + x\text{H}_2\text{O} \to \text{Fe}_3\text{O}_4 + y\text{H}_2$, the values of $x$ and $y$ are:
(A) x = 2, y = 2
(B) x = 4, y = 4
(C) x = 3, y = 4
(D) x = 4, y = 2
✅ Correct Answer: (B) x = 4, y = 4
Explanation: To balance 4 oxygen atoms in $\text{Fe}_3\text{O}_4$, $x=4$ ($4\text{H}_2\text{O}$). This yields 8 hydrogen atoms, giving $y=4$ ($4\text{H}_2$).
Explanation: To balance 4 oxygen atoms in $\text{Fe}_3\text{O}_4$, $x=4$ ($4\text{H}_2\text{O}$). This yields 8 hydrogen atoms, giving $y=4$ ($4\text{H}_2$).
4. The chemical formula of quicklime (calcium oxide) is:
(A) $\text{Ca(OH)}_2$
(B) $\text{CaCO}_3$
(C) $\text{CaO}$
(D) $\text{CaCl}_2$
✅ Correct Answer: (C) $\text{CaO}$
Explanation: Quicklime is calcium oxide with formula CaO. When reacted with water, it forms slaked lime, $\text{Ca(OH)}_2$.
Explanation: Quicklime is calcium oxide with formula CaO. When reacted with water, it forms slaked lime, $\text{Ca(OH)}_2$.
5. What is the chemical formula of limestone and marble?
(A) $\text{CaO}$
(B) $\text{Ca(OH)}_2$
(C) $\text{CaCO}_3$
(D) $\text{CaSO}_4$
✅ Correct Answer: (C) $\text{CaCO}_3$
Explanation: Limestone, marble, chalk, and eggshells primarily consist of calcium carbonate ($\text{CaCO}_3$).
Explanation: Limestone, marble, chalk, and eggshells primarily consist of calcium carbonate ($\text{CaCO}_3$).
6. Which of the following is an endothermic reaction?
(A) Combustion of natural gas
(B) Respiration
(C) Reaction of quicklime with water
(D) Thermal decomposition of calcium carbonate
✅ Correct Answer: (D) Thermal decomposition of calcium carbonate
Explanation: Decomposition of limestone requires absorption of heat energy ($\Delta$), making it an endothermic reaction.
Explanation: Decomposition of limestone requires absorption of heat energy ($\Delta$), making it an endothermic reaction.
7. Cellular respiration is classified as an:
(A) Endothermic combination reaction
(B) Exothermic oxidation reaction
(C) Decomposition reduction reaction
(D) Physical reaction
✅ Correct Answer: (B) Exothermic oxidation reaction
Explanation: Respiration involves the slow oxidation of glucose with oxygen, releasing carbon dioxide, water, and substantial ATP energy, making it exothermic.
Explanation: Respiration involves the slow oxidation of glucose with oxygen, releasing carbon dioxide, water, and substantial ATP energy, making it exothermic.
8. Packaged food containing oil and fat is flushed with nitrogen gas to prevent:
(A) Corrosion
(B) Rancidity
(C) Evaporation
(D) Fermentation
✅ Correct Answer: (B) Rancidity
Explanation: Nitrogen is an inert gas that displaces oxygen from the pouch, preventing oxidation (rancidity) of oils and fats.
Explanation: Nitrogen is an inert gas that displaces oxygen from the pouch, preventing oxidation (rancidity) of oils and fats.
9. When a magnesium ribbon burns in air, it produces a dazzling flame of colour:
(A) Bright Yellow
(B) Dazzling White
(C) Blue
(D) Crimson Red
✅ Correct Answer: (B) Dazzling White
Explanation: Magnesium burns with a brilliant dazzling white flame and leaves behind a white powder of magnesium oxide (MgO).
Explanation: Magnesium burns with a brilliant dazzling white flame and leaves behind a white powder of magnesium oxide (MgO).
10. Thermal decomposition of lead nitrate releases characteristic brown fumes of:
(A) Lead oxide
(B) Oxygen gas
(C) Nitrogen dioxide ($\text{NO}_2$)
(D) Nitrogen monoxide
✅ Correct Answer: (C) Nitrogen dioxide ($\text{NO}_2$)
Explanation: Decomposition of $2\text{Pb(NO}_3)_2$ produces pungent brown fumes of nitrogen dioxide ($\text{NO}_2$) gas along with yellow PbO.
Explanation: Decomposition of $2\text{Pb(NO}_3)_2$ produces pungent brown fumes of nitrogen dioxide ($\text{NO}_2$) gas along with yellow PbO.
11. Activity 1.2: When potassium iodide is added to lead nitrate solution, the colour of the precipitate formed is:
(A) White
(B) Yellow
(C) Blue
(D) Black
✅ Correct Answer: (B) Yellow
Explanation: Lead nitrate and potassium iodide react to form an insoluble bright yellow precipitate of lead iodide ($\text{PbI}_2$).
Explanation: Lead nitrate and potassium iodide react to form an insoluble bright yellow precipitate of lead iodide ($\text{PbI}_2$).
12. Activity 1.3: Action of dilute sulphuric acid on zinc granules releases a gas that burns with a:
(A) Sweet aroma
(B) Pop sound
(C) Smoky flame
(D) Green flame
✅ Correct Answer: (B) Pop sound
Explanation: $\text{Zn} + \text{H}_2\text{SO}_4 \to \text{ZnSO}_4 + \text{H}_2\uparrow$. Hydrogen gas burns with a characteristic ‘pop’ sound.
Explanation: $\text{Zn} + \text{H}_2\text{SO}_4 \to \text{ZnSO}_4 + \text{H}_2\uparrow$. Hydrogen gas burns with a characteristic ‘pop’ sound.
13. Activity 1.5: Heating green ferrous sulphate crystals releases gases with the characteristic smell of:
(A) Rotten eggs
(B) Burning sulphur
(C) Ammonia
(D) Vinegar
✅ Correct Answer: (B) Burning sulphur
Explanation: The decomposition of $\text{FeSO}_4$ releases $\text{SO}_2$ and $\text{SO}_3$, which have the suffocating smell of burning sulphur.
Explanation: The decomposition of $\text{FeSO}_4$ releases $\text{SO}_2$ and $\text{SO}_3$, which have the suffocating smell of burning sulphur.
14. Activity 1.7: During electrolysis of water, the volume ratio of hydrogen collected at cathode to oxygen at anode is:
(A) 1 : 1
(B) 2 : 1
(C) 1 : 2
(D) 8 : 1
✅ Correct Answer: (B) 2 : 1
Explanation: Water ($2\text{H}_2\text{O}$) decomposes into 2 volumes of $\text{H}_2$ at cathode and 1 volume of $\text{O}_2$ at anode (ratio $2:1$).
Explanation: Water ($2\text{H}_2\text{O}$) decomposes into 2 volumes of $\text{H}_2$ at cathode and 1 volume of $\text{O}_2$ at anode (ratio $2:1$).
15. Activity 1.8: White silver chloride turns grey in sunlight due to the formation of:
(A) Silver oxide
(B) Silver metal by photolysis
(C) Chlorine gas absorption
(D) Silver nitrate
✅ Correct Answer: (B) Silver metal by photolysis
Explanation: In sunlight, silver chloride decomposes into elemental silver metal (grey) and chlorine gas ($2\text{AgCl} \to 2\text{Ag} + \text{Cl}_2$).
Explanation: In sunlight, silver chloride decomposes into elemental silver metal (grey) and chlorine gas ($2\text{AgCl} \to 2\text{Ag} + \text{Cl}_2$).
16. Which chemical compounds are used in black and white photography?
(A) $\text{AgCl}$ and $\text{AgBr}$
(B) $\text{NaCl}$ and $\text{KCl}$
(C) $\text{CuSO}_4$
(D) $\text{FeSO}_4$
✅ Correct Answer: (A) $\text{AgCl}$ and $\text{AgBr}$
Explanation: Silver halides, specifically silver chloride (AgCl) and silver bromide (AgBr), are used in black and white photography due to photolytic decomposition.
Explanation: Silver halides, specifically silver chloride (AgCl) and silver bromide (AgBr), are used in black and white photography due to photolytic decomposition.
17. Activity 1.9: An iron nail immersed in copper sulphate solution causes the blue colour of the solution to turn:
(A) Colourless
(B) Pale green
(C) Dark red
(D) Deep violet
✅ Correct Answer: (B) Pale green
Explanation: Iron displaces copper from $\text{CuSO}_4$ to form ferrous sulphate ($\text{FeSO}_4$), which imparts a pale green colour to the solution.
Explanation: Iron displaces copper from $\text{CuSO}_4$ to form ferrous sulphate ($\text{FeSO}_4$), which imparts a pale green colour to the solution.
18. Activity 1.11: Heating copper powder in a china dish forms a black surface coating because:
(A) Copper is reduced
(B) Copper(II) oxide (CuO) is formed
(C) Copper carbonate forms
(D) Soot deposits from burner
✅ Correct Answer: (B) Copper(II) oxide (CuO) is formed
Explanation: Copper combines with atmospheric oxygen on heating to form black copper(II) oxide ($2\text{Cu} + \text{O}_2 \xrightarrow{\Delta} 2\text{CuO}$).
Explanation: Copper combines with atmospheric oxygen on heating to form black copper(II) oxide ($2\text{Cu} + \text{O}_2 \xrightarrow{\Delta} 2\text{CuO}$).
19. Assertion (A): Galvanisation is used to protect iron articles from rusting.
Reason (R): Zinc is more reactive than iron and forms a protective oxide coating.
(A) Both (A) and (R) are true and (R) is the correct explanation of (A).
(B) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(C) (A) is true but (R) is false.
(D) (A) is false but (R) is true.
✅ Correct Answer: (A) Both (A) and (R) are true and (R) is the correct explanation of (A).
Explanation: Both statements are correct and (R) correctly explains that zinc acts as a sacrificial anode, preventing iron from rusting.
Explanation: Both statements are correct and (R) correctly explains that zinc acts as a sacrificial anode, preventing iron from rusting.
20. Assertion (A): Cellular respiration is an endothermic reaction.
Reason (R): In respiration, glucose breaks down in cells to release energy.
(A) Both (A) and (R) are true and (R) is the correct explanation of (A).
(B) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(C) (A) is true but (R) is false.
(D) (A) is false but (R) is true.
✅ Correct Answer: (D) (A) is false but (R) is true.
Explanation: Assertion (A) is false because cellular respiration releases energy and is exothermic. Reason (R) is a true statement.
Explanation: Assertion (A) is false because cellular respiration releases energy and is exothermic. Reason (R) is a true statement.
21. Assertion (A): Passing carbon dioxide gas through lime water turns it milky.
Reason (R): Insoluble calcium carbonate is formed.
(A) Both (A) and (R) are true and (R) is the correct explanation of (A).
(B) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(C) (A) is true but (R) is false.
(D) (A) is false but (R) is true.
✅ Correct Answer: (A) Both (A) and (R) are true and (R) is the correct explanation of (A).
Explanation: $\text{Ca(OH)}_2 + \text{CO}_2 \to \text{CaCO}_3\downarrow + \text{H}_2\text{O}$. Insoluble white calcium carbonate causes the milky turbidity.
Explanation: $\text{Ca(OH)}_2 + \text{CO}_2 \to \text{CaCO}_3\downarrow + \text{H}_2\text{O}$. Insoluble white calcium carbonate causes the milky turbidity.
22. Assertion (A): Decomposition reactions are termed the opposite of combination reactions.
Reason (R): In decomposition, a single compound splits into simpler substances, whereas in combination, two or more reactants yield a single product.
(A) Both (A) and (R) are true and (R) is the correct explanation of (A).
(B) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(C) (A) is true but (R) is false.
(D) (A) is false but (R) is true.
✅ Correct Answer: (A) Both (A) and (R) are true and (R) is the correct explanation of (A).
Explanation: Both statements are true and Reason (R) provides the exact definition and contrast between combination and decomposition.
Explanation: Both statements are true and Reason (R) provides the exact definition and contrast between combination and decomposition.
23. Assertion (A): A silver coin placed in copper sulphate solution displaces copper.
Reason (R): Silver is more reactive than copper in the activity series.
(A) Both (A) and (R) are true and (R) is the correct explanation of (A).
(B) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(C) (A) is true but (R) is false.
(D) Both (A) and (R) are false.
✅ Correct Answer: (D) Both (A) and (R) are false.
Explanation: Silver is less reactive than copper and cannot displace copper from its salt solution. Both Assertion and Reason are false.
Explanation: Silver is less reactive than copper and cannot displace copper from its salt solution. Both Assertion and Reason are false.
24. Assertion (A): Rancidity causes unpleasant odor and stale taste in fried snacks.
Reason (R): Antioxidants accelerate the oxidation process of fatty acids in food.
(A) Both (A) and (R) are true and (R) is the correct explanation of (A).
(B) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(C) (A) is true but (R) is false.
(D) (A) is false but (R) is true.
✅ Correct Answer: (C) (A) is true but (R) is false.
Explanation: Assertion is true. Reason is false because antioxidants retard and prevent the oxidation of fats rather than accelerating it.
Explanation: Assertion is true. Reason is false because antioxidants retard and prevent the oxidation of fats rather than accelerating it.
25. In the redox reaction $\text{MnO}_2 + 4\text{HCl} \to \text{MnCl}_2 + 2\text{H}_2\text{O} + \text{Cl}_2$, the reducing agent is:
(A) $\text{MnO}_2$
(B) $\text{HCl}$
(C) $\text{MnCl}_2$
(D) $\text{Cl}_2$
✅ Correct Answer: (B) $\text{HCl}$
Explanation: HCl loses hydrogen to form $\text{Cl}_2$ (gets oxidised). The substance that is oxidised acts as the reducing agent.
Explanation: HCl loses hydrogen to form $\text{Cl}_2$ (gets oxidised). The substance that is oxidised acts as the reducing agent.
26. Why are a few drops of dilute sulphuric acid added to water before electrolysis?
(A) To color the water
(B) To enhance electrical conductivity of water
(C) To prevent oxygen formation
(D) To clean the electrodes
✅ Correct Answer: (B) To enhance electrical conductivity of water
Explanation: Pure distilled water is a poor conductor of electricity. Adding acid provides ions ($\text{H}^+, \text{SO}_4^{2-}$), making it a good conductor.
Explanation: Pure distilled water is a poor conductor of electricity. Adding acid provides ions ($\text{H}^+, \text{SO}_4^{2-}$), making it a good conductor.
27. Combustion of natural gas (methane) is an example of:
(A) Endothermic decomposition
(B) Exothermic combination
(C) Exothermic oxidation reaction
(D) Double displacement
✅ Correct Answer: (C) Exothermic oxidation reaction
Explanation: $\text{CH}_4 + 2\text{O}_2 \to \text{CO}_2 + 2\text{H}_2\text{O} + \text{Heat}$. It is an exothermic oxidation reaction.
Explanation: $\text{CH}_4 + 2\text{O}_2 \to \text{CO}_2 + 2\text{H}_2\text{O} + \text{Heat}$. It is an exothermic oxidation reaction.
28. The lustrous, shiny white finish on walls appears 2-3 days after whitewashing due to the formation of:
(A) $\text{CaO}$
(B) $\text{Ca(OH)}_2$
(C) $\text{CaCO}_3$
(D) $\text{CaSO}_4$
✅ Correct Answer: (C) $\text{CaCO}_3$
Explanation: Slaked lime $\text{Ca(OH)}_2$ reacts slowly with airborne $\text{CO}_2$ to form a hard, lustrous layer of calcium carbonate ($\text{CaCO}_3$).
Explanation: Slaked lime $\text{Ca(OH)}_2$ reacts slowly with airborne $\text{CO}_2$ to form a hard, lustrous layer of calcium carbonate ($\text{CaCO}_3$).
29. The chemical formula for rust is:
(A) $\text{FeO}$
(B) $\text{Fe}_3\text{O}_4$
(C) $\text{Fe}_2\text{O}_3 \cdot x\text{H}_2\text{O}$
(D) $\text{Fe(OH)}_2$
✅ Correct Answer: (C) $\text{Fe}_2\text{O}_3 \cdot x\text{H}_2\text{O}$
Explanation: Rust is hydrated iron(III) oxide with the formula $\text{Fe}_2\text{O}_3 \cdot x\text{H}_2\text{O}$.
Explanation: Rust is hydrated iron(III) oxide with the formula $\text{Fe}_2\text{O}_3 \cdot x\text{H}_2\text{O}$.
30. What happens when hydrogen gas is passed over hot black copper(II) oxide?
(A) No reaction occurs
(B) The black surface turns reddish-brown copper
(C) A yellow precipitate forms
(D) It turns green
✅ Correct Answer: (B) The black surface turns reddish-brown copper
Explanation: $\text{CuO (black)} + \text{H}_2 \xrightarrow{\Delta} \text{Cu (brown)} + \text{H}_2\text{O}$. Copper oxide is reduced back to brown metallic copper.
Explanation: $\text{CuO (black)} + \text{H}_2 \xrightarrow{\Delta} \text{Cu (brown)} + \text{H}_2\text{O}$. Copper oxide is reduced back to brown metallic copper.
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