{"id":12819,"date":"2025-09-23T13:03:15","date_gmt":"2025-09-23T12:03:15","guid":{"rendered":"https:\/\/mcqsadda.com\/?p=12819"},"modified":"2025-10-22T10:38:30","modified_gmt":"2025-10-22T09:38:30","slug":"chemical-reactions-top-100-mcqs-with-answer-and-explanation","status":"publish","type":"post","link":"https:\/\/mcqsadda.com\/index.php\/2025\/09\/23\/chemical-reactions-top-100-mcqs-with-answer-and-explanation\/","title":{"rendered":"Chemical Reactions Top 100 MCQs With Answer and Explanation"},"content":{"rendered":"\n

1. A chemical reaction involves:
<\/mark><\/strong>A) Breaking and forming of bonds
B) Only breaking of bonds
C) Only forming of bonds
D) Change in physical state only
Answer:<\/strong> A
Explanation:<\/strong> Chemical reactions occur by breaking old bonds and forming new ones.<\/p>\n\n\n\n

2. Which of the following is not<\/em> a chemical reaction?
<\/mark><\/strong>A) Rusting of iron
B) Burning of paper
C) Melting of ice
D) Respiration
Answer:<\/strong> C
Explanation:<\/strong> Melting of ice is a physical change, not a chemical reaction.<\/p>\n\n\n\n

3. Which of the following is a chemical reaction?
<\/mark><\/strong>A) Dissolving sugar in water
B) Lighting a candle
C) Boiling water
D) Cutting paper
Answer:<\/strong> B
Explanation:<\/strong> Lighting a candle involves combustion \u2192 chemical reaction.<\/p>\n\n\n\n

4. Which of the following represents a decomposition reaction?
<\/mark><\/strong>A) 2H\u2082 + O\u2082 \u2192 2H\u2082O
B) CaCO\u2083 \u2192 CaO + CO\u2082
C) Zn + H\u2082SO\u2084 \u2192 ZnSO\u2084 + H\u2082
D) NaOH + HCl \u2192 NaCl + H\u2082O
Answer:<\/strong> B
Explanation:<\/strong> CaCO\u2083 breaks into CaO and CO\u2082 \u2192 decomposition.<\/p>\n\n\n\n

5. A reaction in which heat is released is called:
<\/mark><\/strong>A) Endothermic reaction
B) Exothermic reaction
C) Photochemical reaction
D) Catalytic reaction
Answer:<\/strong> B
Explanation:<\/strong> Exothermic reactions release heat energy (e.g., combustion).<\/p>\n\n\n\n

6. Which of the following is an endothermic reaction?
<\/mark><\/strong>A) Combustion of coal
B) Respiration
C) Photosynthesis
D) Neutralization
Answer:<\/strong> C
Explanation:<\/strong> Photosynthesis absorbs sunlight \u2192 endothermic.<\/p>\n\n\n\n

7. Which reaction is used in black and white photography?
<\/mark><\/strong>A) Decomposition of AgBr
B) Combination of H\u2082 + O\u2082
C) Neutralization of acid and base
D) Combustion of methane
Answer:<\/strong> A
Explanation:<\/strong> Light decomposes AgBr \u2192 Ag + Br\u2082 (photochemical reaction).<\/p>\n\n\n\n

8. Rusting of iron is an example of:
<\/mark><\/strong>A) Oxidation
B) Reduction
C) Neutralization
D) Precipitation
Answer:<\/strong> A
Explanation:<\/strong> Iron reacts with oxygen and moisture \u2192 Fe\u2082O\u2083\u00b7xH\u2082O (rust).<\/p>\n\n\n\n

9. The reaction between acid and base is called:
<\/mark><\/strong>A) Combustion
B) Neutralization
C) Reduction
D) Precipitation
Answer:<\/strong> B
Explanation:<\/strong> Acid + Base \u2192 Salt + Water = neutralization.<\/p>\n\n\n\n

10. Which of the following is a redox reaction?
<\/mark><\/strong>A) Zn + CuSO\u2084 \u2192 ZnSO\u2084 + Cu
B) HCl + NaOH \u2192 NaCl + H\u2082O
C) AgNO\u2083 + NaCl \u2192 AgCl + NaNO\u2083
D) CaCO\u2083 \u2192 CaO + CO\u2082
Answer:<\/strong> A
Explanation:<\/strong> Zn oxidized, Cu\u00b2\u207a reduced \u2192 redox.<\/p>\n\n\n\n

11. Which of the following is a combination reaction?
<\/mark><\/strong>A) 2H\u2082 + O\u2082 \u2192 2H\u2082O
B) CaCO\u2083 \u2192 CaO + CO\u2082
C) Zn + H\u2082SO\u2084 \u2192 ZnSO\u2084 + H\u2082
D) AgNO\u2083 + NaCl \u2192 AgCl + NaNO\u2083
Answer:<\/strong> A
Explanation:<\/strong> Two elements combine \u2192 water.<\/p>\n\n\n\n

12. Which of the following is a displacement reaction?
<\/mark><\/strong>A) 2H\u2082 + O\u2082 \u2192 2H\u2082O
B) CuSO\u2084 + Zn \u2192 ZnSO\u2084 + Cu
C) HCl + NaOH \u2192 NaCl + H\u2082O
D) CaCO\u2083 \u2192 CaO + CO\u2082
Answer:<\/strong> B
Explanation:<\/strong> Zn displaces Cu from CuSO\u2084.<\/p>\n\n\n\n

13. Which of the following is an example of precipitation reaction?
<\/mark><\/strong>A) AgNO\u2083 + NaCl \u2192 AgCl + NaNO\u2083
B) HCl + NaOH \u2192 NaCl + H\u2082O
C) 2H\u2082 + O\u2082 \u2192 2H\u2082O
D) CaCO\u2083 \u2192 CaO + CO\u2082
Answer:<\/strong> A
Explanation:<\/strong> AgCl precipitate forms.<\/p>\n\n\n\n

14. A reaction that proceeds with the help of sunlight is called:
<\/mark><\/strong>A) Thermal reaction
B) Photochemical reaction
C) Electrochemical reaction
D) Catalytic reaction
Answer:<\/strong> B
Explanation:<\/strong> Example: Photosynthesis, decomposition of AgCl in sunlight.<\/p>\n\n\n\n

15. The reaction in which an element replaces another in a compound is called:
<\/mark><\/strong>A) Combination
B) Double displacement
C) Single displacement
D) Decomposition
Answer:<\/strong> C
Explanation:<\/strong> One element replaces another \u2192 single displacement.<\/p>\n\n\n\n

16. The process of respiration is:
<\/mark><\/strong>A) Endothermic
B) Exothermic
C) Neutralization
D) Photochemical
Answer:<\/strong> B
Explanation:<\/strong> Respiration releases energy \u2192 exothermic.<\/p>\n\n\n\n

17. Which of the following is an example of double displacement reaction?
<\/mark><\/strong>A) Zn + CuSO\u2084 \u2192 ZnSO\u2084 + Cu
B) Na\u2082SO\u2084 + BaCl\u2082 \u2192 BaSO\u2084 + 2NaCl
C) 2H\u2082 + O\u2082 \u2192 2H\u2082O
D) CaCO\u2083 \u2192 CaO + CO\u2082
Answer:<\/strong> B
Explanation:<\/strong> Exchange of ions between two compounds.<\/p>\n\n\n\n

18. The burning of methane is an example of:
<\/mark><\/strong>A) Combination
B) Decomposition
C) Neutralization
D) Combustion
Answer:<\/strong> D
Explanation:<\/strong> CH\u2084 + O\u2082 \u2192 CO\u2082 + H\u2082O + heat.<\/p>\n\n\n\n

19. Which is not a type of chemical reaction?
<\/mark><\/strong>A) Combination
B) Decomposition
C) Displacement
D) Rotation
Answer:<\/strong> D
Explanation:<\/strong> Rotation is a physical process.<\/p>\n\n\n\n

20. Respiration is essentially the reverse of:
<\/mark><\/strong>A) Combustion
B) Photosynthesis
C) Electrolysis
D) Oxidation
Answer:<\/strong> B
Explanation:<\/strong> Photosynthesis stores energy, respiration releases it.<\/p>\n\n\n\n

21. Which of the following reactions is endothermic?
<\/mark><\/strong>A) Evaporation of water
B) Photosynthesis
C) Thermal decomposition of CaCO\u2083
D) All of the above
Answer:<\/strong> D
Explanation:<\/strong> All absorb energy.<\/p>\n\n\n\n

22. Which of the following is not<\/em> a characteristic of a chemical reaction?
<\/mark><\/strong>A) Evolution of gas
B) Change in temperature
C) Formation of precipitate
D) Change in shape only
Answer:<\/strong> D
Explanation:<\/strong> Change in shape is a physical change.<\/p>\n\n\n\n

23. The energy required to start a chemical reaction is called:
<\/mark><\/strong>A) Bond energy
B) Lattice energy
C) Activation energy
D) Ionization energy
Answer:<\/strong> C
Explanation:<\/strong> Activation energy initiates reaction.<\/p>\n\n\n\n

24. Which gas is evolved when Zn reacts with dilute H\u2082SO\u2084?
<\/mark><\/strong>A) CO\u2082
B) H\u2082
C) SO\u2082
D) O\u2082
Answer:<\/strong> B
Explanation:<\/strong> Zn + H\u2082SO\u2084 \u2192 ZnSO\u2084 + H\u2082.<\/p>\n\n\n\n

25. When CaO is added to water, the reaction is:<\/mark><\/strong>
A) Endothermic
B) Exothermic
C) Neutralization
D) Decomposition
Answer:<\/strong> B
Explanation:<\/strong> CaO + H\u2082O \u2192 Ca(OH)\u2082 + heat (slaking of lime).<\/p>\n\n\n\n

26. The law used in balancing chemical equations is:
<\/mark><\/strong>A) Law of definite proportion
B) Law of conservation of mass
C) Law of multiple proportion
D) Law of constant energy
Answer:<\/strong> B
Explanation:<\/strong> During reactions, total mass of reactants = mass of products.<\/p>\n\n\n\n

27. The balanced form of: H\u2082 + O\u2082 \u2192 H\u2082O is:
<\/mark><\/strong>A) H\u2082 + O\u2082 \u2192 H\u2082O
B) 2H\u2082 + O\u2082 \u2192 2H\u2082O
C) H\u2082 + 2O\u2082 \u2192 2H\u2082O
D) 2H\u2082 + 2O\u2082 \u2192 H\u2082O\u2082
Answer:<\/strong> B
Explanation:<\/strong> 2 molecules of H\u2082 combine with 1 of O\u2082 \u2192 2H\u2082O.<\/p>\n\n\n\n

28. In the reaction: Zn + CuSO\u2084 \u2192 ZnSO\u2084 + Cu, the oxidizing agent is:
<\/mark><\/strong>A) Zn
B) CuSO\u2084
C) Cu
D) SO\u2084\u00b2\u207b
Answer:<\/strong> B
Explanation:<\/strong> Cu\u00b2\u207a ions in CuSO\u2084 oxidize Zn to Zn\u00b2\u207a.<\/p>\n\n\n\n

29. Oxidation means:
<\/mark><\/strong>A) Loss of electrons
B) Gain of electrons
C) Gain of protons
D) Loss of neutrons
Answer:<\/strong> A
Explanation:<\/strong> Oxidation = loss of electrons, Reduction = gain of electrons.<\/p>\n\n\n\n

30. Reduction means:
<\/mark><\/strong>A) Loss of electrons
B) Gain of electrons
C) Loss of protons
D) Increase in oxidation number
Answer:<\/strong> B
Explanation:<\/strong> Reduction = gain of electrons (decrease in oxidation number).<\/p>\n\n\n\n

31. Which is a redox reaction?
<\/mark><\/strong>A) Zn + 2HCl \u2192 ZnCl\u2082 + H\u2082
B) HCl + NaOH \u2192 NaCl + H\u2082O
C) AgNO\u2083 + NaCl \u2192 AgCl + NaNO\u2083
D) CaCO\u2083 \u2192 CaO + CO\u2082
Answer:<\/strong> A
Explanation:<\/strong> Zn oxidized, H\u207a reduced \u2192 redox.<\/p>\n\n\n\n

32. Which of the following reactions is not<\/em> a redox reaction?
<\/mark><\/strong>A) NaOH + HCl \u2192 NaCl + H\u2082O
B) 2Mg + O\u2082 \u2192 2MgO
C) Fe\u2082O\u2083 + 3CO \u2192 2Fe + 3CO\u2082
D) Zn + CuSO\u2084 \u2192 ZnSO\u2084 + Cu
Answer:<\/strong> A
Explanation:<\/strong> Neutralization has no change in oxidation state.<\/p>\n\n\n\n

33. In the reaction: Fe\u2082O\u2083 + 3CO \u2192 2Fe + 3CO\u2082, the reducing agent is:
<\/mark><\/strong>A) Fe\u2082O\u2083
B) CO
C) Fe
D) CO\u2082
Answer:<\/strong> B
Explanation:<\/strong> CO reduces Fe\u2082O\u2083 to Fe; itself oxidized to CO\u2082.<\/p>\n\n\n\n

34. Which of the following is an exothermic process?
<\/mark><\/strong>A) Photosynthesis
B) Respiration
C) Evaporation
D) Electrolysis
Answer:<\/strong> B
Explanation:<\/strong> Respiration releases energy \u2192 exothermic.<\/p>\n\n\n\n

35. Which is an endothermic process?
<\/mark><\/strong>A) Burning of fuel
B) Neutralization
C) Thermal decomposition of CaCO\u2083
D) Respiration
Answer:<\/strong> C
Explanation:<\/strong> CaCO\u2083 \u2192 CaO + CO\u2082 requires heat input.<\/p>\n\n\n\n

36. The energy change in a chemical reaction is expressed as:
<\/mark><\/strong>A) \u0394S
B) \u0394H
C) \u0394G
D) \u0394P
Answer:<\/strong> B
Explanation:<\/strong> Enthalpy change (\u0394H) measures heat absorbed or released.<\/p>\n\n\n\n

37. A redox reaction always involves:
<\/mark><\/strong>A) Only oxidation
B) Only reduction
C) Both oxidation and reduction simultaneously
D) Neither oxidation nor reduction
Answer:<\/strong> C
Explanation:<\/strong> Redox = oxidation + reduction together.<\/p>\n\n\n\n

38. In the thermite reaction, Fe is obtained from:
<\/mark><\/strong>A) Fe\u2082O\u2083
B) FeSO\u2084
C) FeCl\u2083
D) Fe\u2082(SO\u2084)\u2083
Answer:<\/strong> A
Explanation:<\/strong> Thermite: Fe\u2082O\u2083 + Al \u2192 Al\u2082O\u2083 + Fe.<\/p>\n\n\n\n

39. Thermite reaction is used in:
<\/mark><\/strong>A) Welding of railway tracks
B) Making glass
C) Cooking food
D) Electroplating
Answer:<\/strong> A
Explanation:<\/strong> Exothermic thermite reaction produces molten iron for welding.<\/p>\n\n\n\n

40. In redox reactions, the substance oxidized is called:
<\/mark><\/strong>A) Oxidizing agent
B) Reducing agent
C) Catalyst
D) Neutralizer
Answer:<\/strong> B
Explanation:<\/strong> The one oxidized donates electrons \u2192 reducing agent.<\/p>\n\n\n\n

41. In bleaching powder, the oxidizing property is due to:
<\/mark><\/strong>A) Ca\u00b2\u207a
B) Cl\u2082
C) ClO\u207b
D) O\u2082
Answer:<\/strong> C
Explanation:<\/strong> Bleaching action is due to ClO\u207b ion.<\/p>\n\n\n\n

42. In photosynthesis, CO\u2082 is:
<\/mark><\/strong>A) Oxidized
B) Reduced
C) Neutralized
D) Hydrolyzed
Answer:<\/strong> B
Explanation:<\/strong> CO\u2082 is reduced to glucose using sunlight.<\/p>\n\n\n\n

43. Electrolysis of water gives:
<\/mark><\/strong>A) H\u2082 at cathode, O\u2082 at anode
B) O\u2082 at cathode, H\u2082 at anode
C) H\u2082 + O\u2082 both at cathode
D) H\u2082 + O\u2082 both at anode
Answer:<\/strong> A
Explanation:<\/strong> At cathode \u2192 reduction (H\u2082); at anode \u2192 oxidation (O\u2082).<\/p>\n\n\n\n

44. Oxidation state of sulfur in H\u2082SO\u2084 is:
<\/mark><\/strong>A) +2
B) +4
C) +6
D) \u20132
Answer:<\/strong> C
Explanation:<\/strong> 2(+1) + S + 4(\u20132) = 0 \u2192 S = +6.<\/p>\n\n\n\n

45. Which process involves both oxidation and reduction?
<\/mark><\/strong>A) Electrolysis
B) Neutralization
C) Redox reaction
D) Combustion
Answer:<\/strong> C
Explanation:<\/strong> Oxidation and reduction occur simultaneously in redox.<\/p>\n\n\n\n

46. Combustion of methane is a:
<\/mark><\/strong>A) Decomposition reaction
B) Neutralization reaction
C) Redox reaction
D) Photochemical reaction
Answer:<\/strong> C
Explanation:<\/strong> CH\u2084 + O\u2082 \u2192 CO\u2082 + H\u2082O; C oxidized, O\u2082 reduced.<\/p>\n\n\n\n

47. In the Haber process (N\u2082 + 3H\u2082 \u2192 2NH\u2083), N\u2082 is:
<\/mark><\/strong>A) Oxidized
B) Reduced
C) Both oxidized and reduced
D) Neither
Answer:<\/strong> B
Explanation:<\/strong> N in N\u2082 (0) \u2192 N in NH\u2083 (\u20133) \u2192 reduction.<\/p>\n\n\n\n

48. Which metal is extracted using a displacement reaction?
<\/mark><\/strong>A) Ag from AgNO\u2083
B) Na from NaCl
C) Mg from MgO
D) Al from Al\u2082O\u2083
Answer:<\/strong> A
Explanation:<\/strong> Cu + 2AgNO\u2083 \u2192 Cu(NO\u2083)\u2082 + 2Ag (displacement).<\/p>\n\n\n\n

49. Neutralization reaction is always:
<\/mark><\/strong>A) Exothermic
B) Endothermic
C) Photochemical
D) Reversible
Answer:<\/strong> A
Explanation:<\/strong> Acid + base releases heat \u2192 exothermic.<\/p>\n\n\n\n

50. Which of the following is used in explosives and redox reactions?
<\/mark><\/strong>A) KCl
B) KNO\u2083
C) NaCl
D) NaOH
Answer:<\/strong> B
Explanation:<\/strong> Potassium nitrate (KNO\u2083) is a strong oxidizer, used in gunpowder.<\/p>\n\n\n\n

51. Electrolysis of molten NaCl produces:
<\/mark><\/strong>A) Na at anode, Cl\u2082 at cathode
B) Na at cathode, Cl\u2082 at anode
C) Cl\u2082 at cathode, NaOH at anode
D) H\u2082 at cathode, O\u2082 at anode
Answer:<\/strong> B
Explanation:<\/strong> At cathode \u2192 Na\u207a reduced to Na; at anode \u2192 Cl\u207b oxidized to Cl\u2082.<\/p>\n\n\n\n

52. In a galvanic cell:
<\/mark><\/strong>A) Chemical energy \u2192 Electrical energy
B) Electrical energy \u2192 Chemical energy
C) Heat \u2192 Mechanical energy
D) Light \u2192 Electrical energy
Answer:<\/strong> A
Explanation:<\/strong> Galvanic cell converts chemical energy into electrical energy.<\/p>\n\n\n\n

53. In electrolysis, the electrode where oxidation occurs is:
<\/mark><\/strong>A) Anode
B) Cathode
C) Both
D) None
Answer:<\/strong> A
Explanation:<\/strong> Oxidation occurs at anode, reduction at cathode.<\/p>\n\n\n\n

54. Electroplating is based on:
<\/mark><\/strong>A) Neutralization reaction
B) Photochemical reaction
C) Electrolysis
D) Precipitation
Answer:<\/strong> C
Explanation:<\/strong> Electroplating deposits a thin layer of metal by electrolysis.<\/p>\n\n\n\n

55. Which reaction takes place in photosynthesis?
<\/mark><\/strong>A) CO\u2082 reduced to glucose
B) H\u2082O reduced to O\u2082
C) Glucose oxidized to CO\u2082
D) O\u2082 reduced to CO\u2082
Answer:<\/strong> A
Explanation:<\/strong> Photosynthesis: CO\u2082 reduced to glucose using sunlight.<\/p>\n\n\n\n

56. Which pigment absorbs light energy in photosynthesis?
<\/mark><\/strong>A) Hemoglobin
B) Melanin
C) Chlorophyll
D) Myoglobin
Answer:<\/strong> C
Explanation:<\/strong> Chlorophyll absorbs light and drives photosynthesis.<\/p>\n\n\n\n

57. Which is the reverse of photosynthesis?
<\/mark><\/strong>A) Respiration
B) Combustion
C) Fermentation
D) Electrolysis
Answer:<\/strong> A
Explanation:<\/strong> Respiration breaks down glucose \u2192 CO\u2082 + H\u2082O, opposite of photosynthesis.<\/p>\n\n\n\n

58. Fermentation of glucose produces:
<\/mark><\/strong>A) CO\u2082 and water
B) Ethanol and CO\u2082
C) Methane and water
D) Acetic acid and O\u2082
Answer:<\/strong> B
Explanation:<\/strong> Fermentation: C\u2086H\u2081\u2082O\u2086 \u2192 2C\u2082H\u2085OH + 2CO\u2082.<\/p>\n\n\n\n

59. In the chlor-alkali process, the products are:
<\/mark><\/strong>A) NaOH, Cl\u2082, H\u2082
B) NaCl, H\u2082O, O\u2082
C) Na\u2082CO\u2083, HCl, O\u2082
D) NaOH, O\u2082, NaCl
Answer:<\/strong> A
Explanation:<\/strong> Electrolysis of brine produces NaOH, Cl\u2082, and H\u2082.<\/p>\n\n\n\n

60. Haber\u2019s process involves the reaction:
<\/mark><\/strong>A) N\u2082 + 3H\u2082 \u21cc 2NH\u2083
B) C + O\u2082 \u2192 CO\u2082
C) CaCO\u2083 \u2192 CaO + CO\u2082
D) HCl + NaOH \u2192 NaCl + H\u2082O
Answer:<\/strong> A
Explanation:<\/strong> Haber\u2019s process manufactures NH\u2083.<\/p>\n\n\n\n

61. Which catalyst is used in Haber\u2019s process?
<\/mark><\/strong>A) Pt
B) V\u2082O\u2085
C) Fe
D) Ni
Answer:<\/strong> C
Explanation:<\/strong> Iron catalyst with K\u2082O\/Al\u2082O\u2083 promoters is used.<\/p>\n\n\n\n

62. In Contact process (H\u2082SO\u2084 manufacture), the catalyst is:
<\/mark><\/strong>A) Pt
B) V\u2082O\u2085
C) Fe\u2082O\u2083
D) Ni
Answer:<\/strong> B
Explanation:<\/strong> Vanadium pentoxide catalyzes SO\u2082 \u2192 SO\u2083.<\/p>\n\n\n\n

63. The Ostwald process is used to manufacture:
<\/mark><\/strong>A) HCl
B) HNO\u2083
C) NH\u2083
D) NaOH
Answer:<\/strong> B
Explanation:<\/strong> Ostwald process produces nitric acid (HNO\u2083).<\/p>\n\n\n\n

64. Catalyst used in Ostwald process is:
<\/mark><\/strong>A) V\u2082O\u2085
B) Ni
C) Pt-Rh gauze
D) Fe
Answer:<\/strong> C
Explanation:<\/strong> Pt-Rh gauze catalyzes oxidation of NH\u2083.<\/p>\n\n\n\n

65. Fermentation of milk to curd is due to:
<\/mark><\/strong>A) Yeast
B) Lactobacillus
C) Virus
D) Fungi
Answer:<\/strong> B
Explanation:<\/strong> Lactic acid bacteria (Lactobacillus) convert lactose \u2192 lactic acid.<\/p>\n\n\n\n

66. Which industrial process involves polymerization?
<\/mark><\/strong>A) Haber process
B) Contact process
C) Ziegler\u2013Natta process
D) Ostwald process
Answer:<\/strong> C
Explanation:<\/strong> Ziegler\u2013Natta process produces polymers like polyethylene.<\/p>\n\n\n\n

67. Respiration is essentially a:<\/mark><\/strong>
A) Redox reaction
B) Precipitation reaction
C) Photochemical reaction
D) Neutralization
Answer:<\/strong> A
Explanation:<\/strong> Glucose oxidized, O\u2082 reduced \u2192 redox.<\/p>\n\n\n\n

68. Which of the following is an example of photochemical reaction?
<\/mark><\/strong>A) Photosynthesis
B) Decomposition of AgCl in sunlight
C) Formation of ozone
D) All of the above
Answer:<\/strong> D
Explanation:<\/strong> All are light-driven reactions.<\/p>\n\n\n\n

69. Which gas is released during photosynthesis?
<\/mark><\/strong>A) CO\u2082
B) O\u2082
C) N\u2082
D) H\u2082
Answer:<\/strong> B
Explanation:<\/strong> O\u2082 is released as a by-product.<\/p>\n\n\n\n

70. In respiration, glucose is broken down into:
<\/mark><\/strong>A) CO\u2082 + H\u2082O
B) CO\u2082 + O\u2082
C) CO + H\u2082
D) H\u2082 + O\u2082
Answer:<\/strong> A
Explanation:<\/strong> C\u2086H\u2081\u2082O\u2086 + O\u2082 \u2192 CO\u2082 + H\u2082O + energy.<\/p>\n\n\n\n

71. The chemical reaction in a dry cell is a:
<\/mark><\/strong>A) Combustion reaction
B) Redox reaction
C) Neutralization
D) Photochemical reaction
Answer:<\/strong> B
Explanation:<\/strong> Zinc is oxidized, MnO\u2082 reduced \u2192 redox.<\/p>\n\n\n\n

72. Electrolysis of water is an example of:
<\/mark><\/strong>A) Combination reaction
B) Decomposition reaction
C) Double displacement reaction
D) Neutralization
Answer:<\/strong> B
Explanation:<\/strong> Water decomposes \u2192 H\u2082 and O\u2082.<\/p>\n\n\n\n

73. Which biological reaction is exothermic?
<\/mark><\/strong>A) Photosynthesis
B) DNA replication
C) Respiration
D) Protein synthesis
Answer:<\/strong> C
Explanation:<\/strong> Respiration releases energy \u2192 exothermic.<\/p>\n\n\n\n

74. Which chemical reaction is responsible for ozone formation in the atmosphere?
<\/mark><\/strong>A) CO\u2082 + H\u2082O \u2192 H\u2082CO\u2083
B) O\u2082 + UV \u2192 2O
C) O + O\u2082 \u2192 O\u2083
D) Both B and C
Answer:<\/strong> D
Explanation:<\/strong> UV splits O\u2082 \u2192 O; then O + O\u2082 \u2192 O\u2083.<\/p>\n\n\n\n

75. Which reaction in the body releases energy in ATP form?
<\/mark><\/strong>A) Respiration
B) Photosynthesis
C) Fermentation
D) Electrolysis
Answer:<\/strong> A
Explanation:<\/strong> Cellular respiration releases energy stored as ATP.<\/p>\n\n\n\n

76. Which type of reaction is responsible for acid rain?
<\/mark><\/strong>A) Neutralization
B) Combustion of fossil fuels
C) Electrolysis
D) Displacement
Answer:<\/strong> B
Explanation:<\/strong> SO\u2082 and NOx formed from combustion react with water to form acids \u2192 acid rain.<\/p>\n\n\n\n

77. Corrosion of metals is essentially a:
<\/mark><\/strong>A) Physical change
B) Redox reaction
C) Precipitation reaction
D) Neutralization
Answer:<\/strong> B
Explanation:<\/strong> Corrosion involves oxidation of metals (e.g., Fe \u2192 rust).<\/p>\n\n\n\n

78. The reaction: 2KClO\u2083 \u2192 2KCl + 3O\u2082 is an example of:
<\/mark><\/strong>A) Combination
B) Decomposition
C) Neutralization
D) Displacement
Answer:<\/strong> B
Explanation:<\/strong> KClO\u2083 decomposes on heating to give O\u2082.<\/p>\n\n\n\n

79. Which is an example of a displacement reaction used in daily life?
<\/mark><\/strong>A) Rusting of iron
B) Silver plating of ornaments using Cu
C) Burning of LPG
D) Photosynthesis
Answer:<\/strong> B
Explanation:<\/strong> Cu + 2AgNO\u2083 \u2192 Cu(NO\u2083)\u2082 + 2Ag, used in silver plating.<\/p>\n\n\n\n

80. Which type of reaction occurs in a blast furnace for iron extraction?
<\/mark><\/strong>A) Combination
B) Reduction
C) Neutralization
D) Decomposition
Answer:<\/strong> B
Explanation:<\/strong> Fe\u2082O\u2083 is reduced to Fe by CO.<\/p>\n\n\n\n

81. Which chemical reaction is responsible for global warming?
<\/mark><\/strong>A) Formation of H\u2082O
B) Combustion of fossil fuels producing CO\u2082
C) Neutralization of acids and bases
D) Ozone formation
Answer:<\/strong> B
Explanation:<\/strong> Excess CO\u2082 from combustion \u2192 greenhouse effect.<\/p>\n\n\n\n

82. Which reaction is used in fire extinguishers?
<\/mark><\/strong>A) Na\u2082CO\u2083 + HCl \u2192 NaCl + H\u2082O + CO\u2082
B) K\u2082CO\u2083 + H\u2082O \u2192 KOH + CO\u2082
C) CaCO\u2083 \u2192 CaO + CO\u2082
D) C + O\u2082 \u2192 CO\u2082
Answer:<\/strong> A
Explanation:<\/strong> CO\u2082 released smothers fire.<\/p>\n\n\n\n

83. Which reaction occurs in nuclear power plants?
<\/mark><\/strong>A) Chemical redox reaction
B) Fission reaction
C) Fusion reaction
D) Displacement
Answer:<\/strong> B
Explanation:<\/strong> Nuclear fission of U-235 releases energy (not chemical but linked to energy production).<\/p>\n\n\n\n

84. Burning of coal mainly produces:
<\/mark><\/strong>A) H\u2082O
B) CO\u2082
C) O\u2082
D) H\u2082
Answer:<\/strong> B
Explanation:<\/strong> Carbon burns in oxygen \u2192 CO\u2082.<\/p>\n\n\n\n

85. The reaction responsible for smog formation is:
<\/mark><\/strong>A) NOx + hydrocarbons + sunlight
B) CO\u2082 + O\u2082
C) SO\u2082 + H\u2082O
D) HCl + NH\u2083
Answer:<\/strong> A
Explanation:<\/strong> Photochemical reaction of NOx and hydrocarbons \u2192 smog.<\/p>\n\n\n\n

86. Which of the following is an oxidation reaction?
<\/mark><\/strong>A) Fe\u00b2\u207a \u2192 Fe\u00b3\u207a
B) Cl\u2082 \u2192 2Cl\u207b
C) Cu\u00b2\u207a \u2192 Cu
D) MnO\u2082 \u2192 Mn\u00b2\u207a
Answer:<\/strong> A
Explanation:<\/strong> Fe\u00b2\u207a loses one electron \u2192 oxidation.<\/p>\n\n\n\n

87. Which of the following is a reduction reaction?
<\/mark><\/strong>A) Zn \u2192 Zn\u00b2\u207a
B) O\u2082 \u2192 O\u00b2\u207b
C) Fe\u00b2\u207a \u2192 Fe\u00b3\u207a
D) Cl\u207b \u2192 Cl\u2082
Answer:<\/strong> B
Explanation:<\/strong> O\u2082 gains electrons \u2192 reduced.<\/p>\n\n\n\n

88. Combustion of hydrogen gives:
<\/mark><\/strong>A) H\u2082O
B) CO\u2082
C) H\u2082O\u2082
D) H\u2082O + CO\u2082
Answer:<\/strong> A
Explanation:<\/strong> 2H\u2082 + O\u2082 \u2192 2H\u2082O.<\/p>\n\n\n\n

89. Which type of chemical reaction releases maximum energy?
<\/mark><\/strong>A) Neutralization
B) Combustion
C) Displacement
D) Precipitation
Answer:<\/strong> B
Explanation:<\/strong> Combustion releases large amounts of heat and light.<\/p>\n\n\n\n

90. The process of tarnishing of silver is due to:
<\/mark><\/strong>A) SO\u2082
B) H\u2082S
C) CO\u2082
D) O\u2082
Answer:<\/strong> B
Explanation:<\/strong> Ag + H\u2082S \u2192 Ag\u2082S (black coating).<\/p>\n\n\n\n

91. Which gas is produced when metals react with acids?
<\/mark><\/strong>A) CO\u2082
B) SO\u2082
C) H\u2082
D) O\u2082
Answer:<\/strong> C
Explanation:<\/strong> Metal + Acid \u2192 Salt + H\u2082.<\/p>\n\n\n\n

92. The green coating on copper articles is due to:
<\/mark><\/strong>A) CuO
B) CuCO\u2083\u00b7Cu(OH)\u2082
C) CuSO\u2084
D) CuCl\u2082
Answer:<\/strong> B
Explanation:<\/strong> Copper reacts with CO\u2082 and H\u2082O \u2192 basic copper carbonate.<\/p>\n\n\n\n

93. Which reaction is used in breathing by scuba divers?
<\/mark><\/strong>A) Decomposition of KClO\u2083
B) Reaction of NaOH with CO\u2082
C) Release of O\u2082 from compressed tanks
D) Displacement of O\u2082 from CuO
Answer:<\/strong> C
Explanation:<\/strong> Divers carry compressed O\u2082 cylinders.<\/p>\n\n\n\n

94. Which reaction explains bleaching action of chlorine?
<\/mark><\/strong>A) Cl\u2082 + H\u2082O \u2192 HCl + HOCl
B) HOCl \u2192 HCl + [O]
C) [O] + Colored substance \u2192 Colorless substance
D) All of the above
Answer:<\/strong> D
Explanation:<\/strong> Chlorine releases nascent oxygen which decolorizes substances.<\/p>\n\n\n\n

95. Which chemical reaction is responsible for depletion of ozone layer?
<\/mark><\/strong>A) CO\u2082 + H\u2082O \u2192 H\u2082CO\u2083
B) CFCs releasing Cl atoms
C) Combustion of coal
D) Rusting of iron
Answer:<\/strong> B
Explanation:<\/strong> CFCs release Cl\u00b7 radicals which destroy ozone molecules.<\/p>\n\n\n\n

96. Which type of reaction is used in making soap?
<\/mark><\/strong>A) Neutralization
B) Saponification
C) Precipitation
D) Displacement
Answer:<\/strong> B
Explanation:<\/strong> Saponification = hydrolysis of fats by alkali to form soap + glycerol.<\/p>\n\n\n\n

97. Which of the following is an industrial redox reaction?
<\/mark><\/strong>A) Extraction of iron from Fe\u2082O\u2083
B) Electrolysis of water
C) Production of Na by Downs cell
D) All of the above
Answer:<\/strong> D
Explanation:<\/strong> All involve oxidation\u2013reduction processes.<\/p>\n\n\n\n

98. The photosynthesis reaction can be written as:
<\/mark><\/strong>A) CO\u2082 + H\u2082O \u2192 C\u2086H\u2081\u2082O\u2086 + O\u2082
B) C\u2086H\u2081\u2082O\u2086 \u2192 CO\u2082 + H\u2082O
C) H\u2082 + O\u2082 \u2192 H\u2082O
D) CO\u2082 + O\u2082 \u2192 CO
Answer:<\/strong> A
Explanation:<\/strong> Photosynthesis forms glucose and oxygen.<\/p>\n\n\n\n

99. Which chemical reaction is reversible?
<\/mark><\/strong>A) Photosynthesis
B) Haber process (N\u2082 + 3H\u2082 \u21cc 2NH\u2083)
C) Combustion of methane
D) Rusting of iron
Answer:<\/strong> B
Explanation:<\/strong> Haber process is reversible, equilibrium-based.<\/p>\n\n\n\n

100. Which statement about chemical reactions is correct?
<\/mark><\/strong>A) They always produce heat
B) They always change state of matter
C) They involve breaking and making of bonds
D) They cannot be reversed
Answer:<\/strong> C
Explanation:<\/strong> The essence of all chemical reactions is bond breaking and bond formation.<\/p>\n","protected":false},"excerpt":{"rendered":"

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