NCERT MCQs Class 10 General Science Chapter 1 Chemical Reactions and Equations
NCERT MCQ of Class 10 General Science Chapter 1 Chemical Reactions and Equations
1. Which of the following is a balanced chemical equation?
(a) H₂ + O₂ → H₂O
(b) 2H₂ + O₂ → 2H₂O
(c) H₂ + 2O₂ → H₂O₂
(d) None of the above
Answer: (b) 2H₂ + O₂ → 2H₂O
Explanation: A balanced chemical equation has equal numbers of each type of atom on both sides. Here, the number of hydrogen and oxygen atoms is balanced.
2. What type of reaction is represented by the equation: Zn + CuSO₄ → ZnSO₄ + Cu?
(a) Combination reaction
(b) Decomposition reaction
(c) Displacement reaction
(d) Double displacement reaction
Answer: (c) Displacement reaction
Explanation: Zinc displaces copper from copper sulfate to form zinc sulfate and copper, making it a displacement reaction.
3. Which of the following is an example of a decomposition reaction?
(a) 2Mg + O₂ → 2MgO
(b) CaCO₃ → CaO + CO₂
(c) H₂ + Cl₂ → 2HCl
(d) NaCl + AgNO₃ → NaNO₃ + AgCl
Answer: (b) CaCO₃ → CaO + CO₂
Explanation: In a decomposition reaction, a compound breaks down into two or more simpler substances. Calcium carbonate decomposes into calcium oxide and carbon dioxide.
4. What is the product formed when magnesium burns in air?
(a) MgCO₃
(b) Mg(OH)₂
(c) MgO
(d) MgCl₂
Answer: (c) MgO
Explanation: When magnesium burns in oxygen, it forms magnesium oxide (MgO).
5. Which of the following reactions is exothermic?
(a) Electrolysis of water
(b) Respiration
(c) Decomposition of calcium carbonate
(d) Melting of ice
Answer: (b) Respiration
Explanation: Respiration releases energy in the form of heat, making it an exothermic reaction.
6. What does a chemical equation convey?
(a) Reactants and products involved
(b) Physical states of substances
(c) Number of molecules involved
(d) All of the above
Answer: (d) All of the above
Explanation: A chemical equation shows the reactants, products, their physical states, and the proportion of molecules or atoms involved.
7. What happens in a precipitation reaction?
(a) Heat is absorbed
(b) A gas is formed
(c) An insoluble solid is formed
(d) A compound is decomposed
Answer: (c) An insoluble solid is formed
Explanation: In a precipitation reaction, two solutions react to form an insoluble solid (precipitate).
8. Which of the following represents a redox reaction?
(a) HCl + NaOH → NaCl + H₂O
(b) Zn + 2HCl → ZnCl₂ + H₂
(c) 2KBr + Cl₂ → 2KCl + Br₂
(d) Both (b) and (c)
Answer: (d) Both (b) and (c)
Explanation: Redox reactions involve oxidation and reduction. In (b), zinc is oxidized, and hydrogen is reduced. In (c), bromide is oxidized, and chlorine is reduced.
9. What is the purpose of a catalyst in a chemical reaction?
(a) To increase the yield of products
(b) To slow down the reaction
(c) To change the products formed
(d) To alter the rate of the reaction without being consumed
Answer: (d) To alter the rate of the reaction without being consumed
Explanation: A catalyst speeds up or slows down a reaction without undergoing any permanent chemical change.
10. What is observed when iron reacts with copper sulfate solution?
(a) No reaction occurs
(b) Iron sulfate is formed, and copper is displaced
(c) A white precipitate is formed
(d) A gas is evolved
Answer: (b) Iron sulfate is formed, and copper is displaced
Explanation: Iron displaces copper from copper sulfate because iron is more reactive than copper.
Which type of reaction is the combustion of methane (CH₄)?
(a) Combination reaction
(b) Displacement reaction
(c) Redox reaction
(d) Neutralization reaction
Answer: (c) Redox reaction
Explanation: During the combustion of methane, CH₄ is oxidized to CO₂, and O₂ is reduced to H₂O, making it a redox reaction.
12. What is the product of the reaction between lead nitrate and potassium iodide?
(a) PbI₂ + KNO₃
(b) Pb(NO₃)₂ + KI
(c) Pb(NO₃)₂ + KCl
(d) PbI₂ + K₂SO₄
Answer: (a) PbI₂ + KNO₃
Explanation: Lead nitrate reacts with potassium iodide to form a yellow precipitate of lead iodide and potassium nitrate.
13. What is the process of coating iron with zinc to prevent rusting called?
(a) Alloying
(b) Electroplating
(c) Galvanization
(d) Oxidation
Answer: (c) Galvanization
Explanation: Galvanization involves coating iron with zinc to prevent rusting by forming a protective layer.
14. Which of the following is a characteristic of a chemical change?
(a) No new substance is formed
(b) It is easily reversible
(c) It involves a change in the composition of substances
(d) It does not involve energy changes
Answer: (c) It involves a change in the composition of substances
Explanation: A chemical change results in the formation of new substances with different compositions and properties.
15. What type of reaction is the rusting of iron?
(a) Combination reaction
(b) Displacement reaction
(c) Redox reaction
(d) Neutralization reaction
Answer: (c) Redox reaction
Explanation: Rusting of iron involves the oxidation of iron and reduction of oxygen, making it a redox process.
16. Which gas is evolved when zinc reacts with dilute hydrochloric acid?
(a) Oxygen
(b) Hydrogen
(c) Chlorine
(d) Carbon dioxide
Answer: (b) Hydrogen
Explanation: Zinc reacts with hydrochloric acid to produce zinc chloride and hydrogen gas.
17. What is the balanced equation for the decomposition of ferrous sulfate?
(a) FeSO₄ → Fe₂O₃ + SO₂
(b) 2FeSO₄ → Fe₂O₃ + SO₂ + SO₃
(c) FeSO₄ → Fe + SO₄
(d) None of the above
Answer: (b) 2FeSO₄ → Fe₂O₃ + SO₂ + SO₃
Explanation: When ferrous sulfate is heated, it decomposes into ferric oxide, sulfur dioxide, and sulfur trioxide.
18. Which compound is formed when carbon dioxide reacts with lime water?
(a) Calcium carbonate
(b) Calcium oxide
(c) Calcium sulfate
(d) Calcium hydroxide
Answer: (a) Calcium carbonate
Explanation: CO₂ reacts with lime water (Ca(OH)₂) to form calcium carbonate (CaCO₃), which appears as a milky precipitate.
19. Which observation indicates that a chemical reaction has occurred?
(a) Change in color
(b) Evolution of gas
(c) Formation of precipitate
(d) All of the above
Answer: (d) All of the above
Explanation: A chemical reaction can be identified by changes like color, gas evolution, or precipitate formation.
20. What type of reaction is represented by the equation: 2Na + Cl₂ → 2NaCl?
(a) Decomposition reaction
(b) Combination reaction
(c) Displacement reaction
(d) Neutralization reaction
Answer: (b) Combination reaction
Explanation: Sodium and chlorine combine to form sodium chloride, making it a combination reaction.
In a redox reaction, the substance that is reduced acts as:
(a) Reducing agent
(b) Oxidizing agent
(c) Catalyst
(d) Neutralizing agent
Answer: (b) Oxidizing agent
Explanation: The substance that is reduced gains electrons and facilitates oxidation, acting as the oxidizing agent.
22. What happens when water is added to quicklime (CaO)?
(a) Hydrogen gas is released
(b) Heat is evolved, and slaked lime (Ca(OH)₂) is formed
(c) Quicklime turns into gypsum
(d) No reaction occurs
Answer: (b) Heat is evolved, and slaked lime (Ca(OH)₂) is formed
Explanation: Quicklime reacts exothermically with water to produce slaked lime.
23. Which reaction is endothermic?
(a) Combustion of methane
(b) Dissolution of ammonium chloride in water
(c) Neutralization of HCl and NaOH
(d) Respiration
Answer: (b) Dissolution of ammonium chloride in water
Explanation: Dissolving ammonium chloride in water absorbs heat, making it endothermic.
24. Which reaction involves a gain of electrons?
(a) Oxidation
(b) Reduction
(c) Combustion
(d) Neutralization
Answer: (b) Reduction
Explanation: Reduction is the gain of electrons by a substance.
25. What is the product of electrolysis of water?
(a) Hydrogen and oxygen
(b) Hydrogen and nitrogen
(c) Oxygen and carbon dioxide
(d) Carbon monoxide and hydrogen
Answer: (a) Hydrogen and oxygen
Explanation: Electrolysis of water decomposes it into hydrogen and oxygen gases.
26. What happens when silver chloride is exposed to sunlight?
(a) It turns black due to decomposition
(b) It turns white due to oxidation
(c) It remains unchanged
(d) It forms a precipitate
Answer: (a) It turns black due to decomposition
Explanation: Silver chloride decomposes to silver and chlorine gas in sunlight.
27. Which type of reaction occurs when an acid reacts with a base?
(a) Combination
(b) Neutralization
(c) Displacement
(d) Decomposition
Answer: (b) Neutralization
Explanation: The reaction between an acid and a base produces salt and water, a neutralization reaction.
28. Why is a solution of HCl in water acidic?
(a) It contains H₂ molecules
(b) It releases OH⁻ ions
(c) It releases H⁺ ions
(d) None of the above
Answer: (c) It releases H⁺ ions
Explanation: The dissociation of HCl in water produces H⁺ ions, making it acidic.
29. What is the chemical formula for rust?
(a) Fe₂O₃·xH₂O
(b) FeO
(c) Fe₃O₄
(d) Fe₂SO₄
Answer: (a) Fe₂O₃·xH₂O
Explanation: Rust is hydrated iron (III) oxide, formed when iron reacts with oxygen and water.
30. Which reaction does not occur in the absence of light?
(a) Photosynthesis
(b) Combustion
(c) Electrolysis of water
(d) Decomposition of ammonium chloride
Answer: (a) Photosynthesis
Explanation: Photosynthesis requires sunlight to convert CO₂ and water into glucose and oxygen.
31. Which of the following is a physical change?
(a) Rusting of iron
(b) Burning of wood
(c) Melting of ice
(d) Souring of milk
Answer: (c) Melting of ice
Explanation: Melting of ice is a physical change as it involves a change in state without altering the chemical composition.
32. What type of reaction occurs in the electrolysis of water?
(a) Displacement
(b) Combination
(c) Decomposition
(d) Neutralization
Answer: (c) Decomposition
Explanation: Electrolysis of water is a decomposition reaction where water is broken down into hydrogen and oxygen gases.
33. What happens when carbon dioxide is bubbled through lime water?
(a) It turns milky
(b) It turns clear
(c) It forms bubbles
(d) No reaction occurs
Answer: (a) It turns milky
Explanation: Carbon dioxide reacts with lime water (Ca(OH)₂) to form calcium carbonate, which appears as a milky precipitate.
34. Which is the correct representation of a displacement reaction?
(a) Na + Cl₂ → NaCl
(b) Zn + CuSO₄ → ZnSO₄ + Cu
(c) AgNO₃ + NaCl → AgCl + NaNO₃
(d) CaCO₃ → CaO + CO₂
Answer: (b) Zn + CuSO₄ → ZnSO₄ + Cu
Explanation: Zinc displaces copper from copper sulfate, making this a displacement reaction.
35. Which of the following is not a characteristic of a chemical reaction?
(a) Change in temperature
(b) Change in state
(c) Formation of new substances
(d) No energy change
Answer: (d) No energy change
Explanation: Chemical reactions often involve energy changes, either absorbing or releasing energy.
36. What happens when hydrochloric acid reacts with sodium hydroxide?
(a) A precipitate is formed
(b) Salt and water are formed
(c) Hydrogen gas is released
(d) No reaction occurs
Answer: (b) Salt and water are formed
Explanation: HCl reacts with NaOH in a neutralization reaction to produce sodium chloride (salt) and water.
37. What is observed when baking soda is added to vinegar?
(a) No reaction occurs
(b) A gas is released
(c) A white precipitate is formed
(d) Heat is absorbed
Answer: (b) A gas is released
Explanation: Baking soda reacts with vinegar to release carbon dioxide gas.
38. Which of the following reactions produces a gas?
(a) NaOH + HCl → NaCl + H₂O
(b) Zn + 2HCl → ZnCl₂ + H₂
(c) CaO + H₂O → Ca(OH)₂
(d) AgNO₃ + NaCl → AgCl + NaNO₃
Answer: (b) Zn + 2HCl → ZnCl₂ + H₂
Explanation: Zinc reacts with hydrochloric acid to produce hydrogen gas.
39. Which type of reaction is involved in photosynthesis?
(a) Endothermic and combination
(b) Exothermic and displacement
(c) Decomposition and redox
(d) Endothermic and redox
Answer: (d) Endothermic and redox
Explanation: Photosynthesis absorbs sunlight (endothermic) and involves redox reactions, with CO₂ being reduced to glucose.
40. Why is it important to balance a chemical equation?
(a) To follow the law of conservation of mass
(b) To make the equation simpler
(c) To show the products of the reaction
(d) To indicate physical states
Answer: (a) To follow the law of conservation of mass
Explanation: Balancing ensures that the mass of reactants equals the mass of products, adhering to the conservation of mass.
41. Which reaction is represented by: 2KClO₃ → 2KCl + 3O₂?
(a) Combination reaction
(b) Displacement reaction
(c) Decomposition reaction
(d) Double displacement reaction
Answer: (c) Decomposition reaction
Explanation: Potassium chlorate decomposes into potassium chloride and oxygen gas upon heating.
42. Which gas is responsible for extinguishing fire?
(a) Oxygen
(b) Carbon dioxide
(c) Nitrogen
(d) Hydrogen
Answer: (b) Carbon dioxide
Explanation: Carbon dioxide displaces oxygen around a fire, extinguishing it.
43. What is the result of heating ammonium dichromate?
(a) It decomposes into nitrogen gas
(b) It forms water vapor
(c) It explodes violently
(d) All of the above
Answer: (d) All of the above
Explanation: Ammonium dichromate decomposes upon heating to release nitrogen gas and water vapor with a vigorous reaction.
44. Which reaction is accompanied by the evolution of heat?
(a) Endothermic reaction
(b) Exothermic reaction
(c) Neutral reaction
(d) Electrolysis
Answer: (b) Exothermic reaction
Explanation: Exothermic reactions release heat energy, making them warm.
45. What is the pH of the solution formed when carbon dioxide is dissolved in water?
(a) Neutral
(b) Acidic
(c) Basic
(d) Highly basic
Answer: (b) Acidic
Explanation: Carbon dioxide reacts with water to form carbonic acid, lowering the pH of the solution.
46. What happens during the corrosion of iron?
(a) It gains electrons
(b) It forms hydrated iron (III) oxide
(c) It undergoes reduction
(d) It becomes more shiny
Answer: (b) It forms hydrated iron (III) oxide
Explanation: Corrosion involves the oxidation of iron, forming rust (hydrated iron (III) oxide).
47. What is an example of a double displacement reaction?
(a) NaCl + AgNO₃ → AgCl + NaNO₃
(b) 2H₂ + O₂ → 2H₂O
(c) CH₄ + O₂ → CO₂ + H₂O
(d) Zn + HCl → ZnCl₂ + H₂
Answer: (a) NaCl + AgNO₃ → AgCl + NaNO₃
Explanation: Two ions are exchanged between reactants in this double displacement reaction.
48. What is observed when magnesium ribbon is burned?
(a) Formation of black powder
(b) Formation of white ash
(c) Formation of a precipitate
(d) No reaction
Answer: (b) Formation of white ash
Explanation: Burning magnesium forms magnesium oxide, seen as a white ash.
49. Which of the following is an oxidation reaction?
(a) Rusting of iron
(b) Melting of ice
(c) Mixing water with sugar
(d) Formation of precipitate
Answer: (a) Rusting of iron
Explanation: Rusting involves the oxidation of iron in the presence of moisture.
50. Which metal does not react with water under normal conditions?
(a) Sodium
(b) Potassium
(c) Aluminium
(d) Calcium
Answer: (c) Aluminium
Explanation: Aluminium forms a protective oxide layer, preventing it from reacting with water under normal conditions.
51. Which of the following is an example of a combination reaction?
(a) CaO + H₂O → Ca(OH)₂
(b) NaCl + AgNO₃ → AgCl + NaNO₃
(c) 2HgO → 2Hg + O₂
(d) Zn + 2HCl → ZnCl₂ + H₂
Answer: (a) CaO + H₂O → Ca(OH)₂
Explanation: In a combination reaction, two or more reactants combine to form a single product, as shown in this equation where calcium oxide and water form calcium hydroxide.
52. Which of the following reactions is an example of a decomposition reaction?
(a) NH₃ + HCl → NH₄Cl
(b) 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂
(c) Zn + CuSO₄ → ZnSO₄ + Cu
(d) 2Na + Cl₂ → 2NaCl
Answer: (b) 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂
Explanation: A decomposition reaction involves breaking down a single compound into simpler substances, as seen in the thermal decomposition of lead nitrate.
53. What type of reaction is represented by: 2KBr + Cl₂ → 2KCl + Br₂?
(a) Combination reaction
(b) Double displacement reaction
(c) Decomposition reaction
(d) Displacement reaction
Answer: (d) Displacement reaction
Explanation: In this reaction, chlorine displaces bromine from potassium bromide, making it a displacement reaction.
54. What is the distinguishing feature of a double displacement reaction?
(a) Heat is absorbed during the reaction.
(b) Two ions exchange places between compounds.
(c) A single compound breaks down.
(d) A gas is always produced.
Answer: (b) Two ions exchange places between compounds.
Explanation: A double displacement reaction involves the exchange of ions between two reactants to form two new compounds.
55. Which of the following is a precipitation reaction?
(a) 2Mg + O₂ → 2MgO
(b) Na₂CO₃ + CaCl₂ → 2NaCl + CaCO₃
(c) Zn + CuSO₄ → ZnSO₄ + Cu
(d) 2KClO₃ → 2KCl + 3O₂
Answer: (b) Na₂CO₃ + CaCl₂ → 2NaCl + CaCO₃
Explanation: A precipitation reaction forms an insoluble solid, calcium carbonate (CaCO3CaCO₃CaCO3), in this case.
56. Which of the following reactions is exothermic?
(a) Decomposition of ammonium chloride
(b) Photosynthesis
(c) Combustion of methane
(d) Electrolysis of water
Answer: (c) Combustion of methane
Explanation: Combustion reactions release energy in the form of heat, making them exothermic.
57. What happens in a neutralization reaction?
(a) An acid reacts with a base to form salt and water.
(b) Two compounds decompose simultaneously.
(c) A single compound breaks down into simpler substances.
(d) Two salts exchange ions to form new products.
Answer: (a) An acid reacts with a base to form salt and water.
Explanation: Neutralization is a reaction between an acid and a base, producing salt and water.
58. Which of the following reactions represents a redox reaction?
(a) CaO + H₂O → Ca(OH)₂
(b) Zn + 2HCl → ZnCl₂ + H₂
(c) NaCl + AgNO₃ → AgCl + NaNO₃
(d) 2HgO → 2Hg + O₂
Answer: (b) Zn + 2HCl → ZnCl₂ + H₂
Explanation: In this reaction, zinc is oxidized, and hydrogen is reduced, making it a redox reaction.
59. Which gas is released during the thermal decomposition of calcium carbonate?
(a) Oxygen
(b) Carbon dioxide
(c) Hydrogen
(d) Nitrogen
Answer: (b) Carbon dioxide
Explanation: Thermal decomposition of calcium carbonate (CaCO3CaCO₃CaCO3) produces calcium oxide (CaOCaOCaO) and carbon dioxide (CO2CO₂CO2) gas.
60. Which type of reaction is rusting of iron?
(a) Combination reaction
(b) Decomposition reaction
(c) Redox reaction
(d) Neutralization reaction
Answer: (c) Redox reaction
Explanation: Rusting involves the oxidation of iron and the reduction of oxygen in the presence of water, making it a redox reaction.
MCQs from the exercise part of the chapter
1. Which of the statements about the reaction below are incorrect?
2PbO(s) + C(s) → 2Pb(s) + CO2 (g)
(a) Lead is getting reduced.
(b) Carbon dioxide is getting oxidised.
(c) Carbon is getting oxidised.
(d) Lead oxide is getting reduced.
(i) (a) and (b)
(ii) (a) and (c)
(iii) (a), (b) and (c)
(iv) all
Answer: (i) (a) and (b)
Explanation:
In the given reaction:
2PbO(s)+C(s)→2Pb(s)+CO2(g)2PbO(s) + C(s) → 2Pb(s) + CO_2(g)2PbO(s)+C(s)→2Pb(s)+CO2(g)Lead (Pb): Lead is getting reduced because lead oxide (PbO) is losing oxygen to form metallic lead. So, statement (a) is correct.
Carbon (C): Carbon is getting oxidized as it gains oxygen to form CO2CO_2CO2. Hence, statement (c) is correct.
Carbon dioxide (CO2CO_2CO2): It is not getting oxidized but rather formed as a product, so statement (b) is incorrect.
Lead oxide (PbO): It is indeed getting reduced, as it loses oxygen, so statement (d) is correct.
Thus, the incorrect statements are (a) and (b), corresponding to option (i).
2. Fe2O3 + 2Al → Al2O3 + 2Fe
The above reaction is an example of a
(a) combination reaction.
(b) double displacement reaction.
(c) decomposition reaction.
(d) displacement reaction.
Answer: (d) displacement reaction
Explanation:
In the reaction:
Fe2O3+2Al→Al2O3+2FeFe_2O_3 + 2Al →
Al_2O_3 + 2FeFe2O3+2Al→Al2O3+2Fe,
Aluminium displaces iron from iron(III) oxide (Fe2O3Fe_2O_3Fe2O3) to form aluminium oxide (Al2O3Al_2O_3Al2O3) and iron (FeFeFe).
This is a displacement reaction, as a more reactive metal (Al) replaces a less reactive metal (Fe) from its compound.
It is not:
(a) Combination reaction: A combination reaction involves two or more substances combining to form a single product.
(b) Double displacement reaction: This involves the exchange of ions between two compounds, which is not occurring here.
(c) Decomposition reaction: Decomposition involves breaking down a single compound into simpler substances, which also does not occur in this reaction.
Hence, the reaction is classified as a displacement reaction.
3. What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.
(a) Hydrogen gas and iron chloride are produced.
(b) Chlorine gas and iron hydroxide are produced.
(c) No reaction takes place.
(d) Iron salt and water are produced.
Answer: (a) Hydrogen gas and iron chloride are produced.
Explanation:
When dilute hydrochloric acid (HClHClHCl) reacts with iron (FeFeFe), the reaction produces hydrogen gas (H2H_2H2) and iron chloride (FeCl2FeCl_2FeCl2):
Fe(s)+2HCl(aq)→FeCl2(aq)+H2(g)Fe(s) + 2HCl(aq) → FeCl_2(aq) + H_2(g)Fe(s)+2HCl(aq)→FeCl2(aq)+H2(g)
(a) Hydrogen gas and iron chloride are produced: This is correct as iron reacts with dilute HClHClHCl to form iron chloride and release hydrogen gas.
(b) Chlorine gas and iron hydroxide are produced: This is incorrect because no chlorine gas or hydroxide is formed.
(c) No reaction takes place: This is incorrect because iron reacts with hydrochloric acid.
(d) Iron salt and water are produced: This is incorrect as water is not a product of the reaction.
Thus, the correct answer is (a).
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