⚗️ Chemical Reactions and Equations – Class 10 Science MCQs

Part 4: HOTS, Numericals & Application-based Questions (Q76–Q100)

Q76. Which of the following is an endothermic reaction?

A. Burning of coal
B. Respiration
C. Photosynthesis
D. Combustion of LPG

✅ Correct Answer: C. Photosynthesis

Explanation: Photosynthesis absorbs sunlight to convert CO₂ + H₂O → glucose + O₂.

Q77. Which of the following equations is balanced?

A. N₂ + 3H₂ → 2NH₃
B. N₂ + H₂ → NH₃
C. N₂ + 2H₂ → 2NH₃
D. 2N₂ + 3H₂ → 2NH₃

✅ Correct Answer: A. N₂ + 3H₂ → 2NH₃

Q78. When calcium oxide reacts with water, it forms:

A. Ca(OH)₂ with evolution of heat
B. CaCO₃ with evolution of heat
C. CaCl₂ with cooling
D. Ca(NO₃)₂ with cooling

✅ Correct Answer: A. Ca(OH)₂ with evolution of heat

Q79. A student adds dilute HCl to Zn granules and observes:

A. No change
B. A gas evolves with effervescence
C. A brown gas is formed
D. A black precipitate appears

✅ Correct Answer: B. A gas evolves with effervescence

Explanation: Reaction → Zn + 2HCl → ZnCl₂ + H₂ (bubbles).

Q80. Which type of reaction is used in whitewashing walls?

A. Combination reaction
B. Decomposition reaction
C. Neutralization
D. Displacement

✅ Correct Answer: A. Combination reaction

Explanation: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O (white coating).

Q81. What mass of oxygen is required to completely react with 4 g of hydrogen to form water?

A. 8 g
B. 16 g
C. 32 g
D. 4 g

✅ Correct Answer: B. 16 g

Explanation: 2H₂ (4 g) + O₂ (32 g) → 2H₂O. Proportion = 4 g H₂ reacts with 32 g O₂. For 4 g H₂ → needs 32 g O₂, but we asked for oxygen required → 32 g.
⚠ Correction: On careful check → 4 g H₂ needs 32 g O₂ → so correct = 32 g (Option C).

Q82. Which of the following represents thermal decomposition?

A. 2KClO₃ → 2KCl + 3O₂
B. NaCl + AgNO₃ → AgCl + NaNO₃
C. Mg + O₂ → MgO
D. Zn + HCl → ZnCl₂ + H₂

✅ Correct Answer: A. 2KClO₃ → 2KCl + 3O₂

Q83. When electricity is passed through water, it decomposes to form:

A. H₂ and O₂
B. H₂O₂
C. H₂ only
D. O₂ only

✅ Correct Answer: A. H₂ and O₂

Q84. In the reaction 2Fe + 3Cl₂ → 2FeCl₃, Fe is:

A. Oxidized
B. Reduced
C. Neutralized
D. Displaced

✅ Correct Answer: A. Oxidized

Q85. Which is an example of exothermic reaction?

A. Photosynthesis
B. Decomposition of CaCO₃
C. Combustion of methane
D. Electrolysis of water

✅ Correct Answer: C. Combustion of methane

Q86. Which observation indicates decomposition of ferrous sulphate on heating?

A. White precipitate
B. Brown fumes of NO₂
C. Green crystals turn brown with SO₂ & SO₃ gases
D. Formation of H₂ gas

✅ Correct Answer: C. Green crystals turn brown with SO₂ & SO₃ gases

Q87. Which of the following is NOT an application of redox reactions?

A. Respiration
B. Photosynthesis
C. Combustion
D. Dissolving sugar in water

✅ Correct Answer: D. Dissolving sugar in water

Q88. Identify the oxidizing agent in: CuO + H₂ → Cu + H₂O

A. Cu
B. CuO
C. H₂
D. H₂O

✅ Correct Answer: B. CuO

Q89. Identify the reducing agent in: CuO + H₂ → Cu + H₂O

A. Cu
B. CuO
C. H₂
D. O₂

✅ Correct Answer: C. H₂

Q90. A shiny brown deposit forms on iron when dipped in CuSO₄ solution. The brown substance is:

A. Fe
B. Cu
C. FeSO₄
D. Fe₂O₃

✅ Correct Answer: B. Cu

Q91. In the reaction Zn + H₂SO₄ → ZnSO₄ + H₂, hydrogen is:

A. Oxidized
B. Reduced
C. Displaced
D. Neutralized

✅ Correct Answer: B. Reduced

Q92. Which type of reaction is CaO + H₂O → Ca(OH)₂?

A. Combination and exothermic
B. Decomposition and endothermic
C. Double displacement
D. Redox

✅ Correct Answer: A. Combination and exothermic

Q93. Which gas turns lime water milky?

A. SO₂
B. CO₂
C. O₂
D. H₂

✅ Correct Answer: B. CO₂

Q94. A student added BaCl₂ solution to Na₂SO₄ solution. A white precipitate was formed. This indicates:

A. Displacement reaction
B. Double displacement reaction (precipitation)
C. Combination reaction
D. Decomposition

✅ Correct Answer: B. Double displacement reaction (precipitation)

Q95. Which of the following equations is incorrectly balanced?

A. Zn + 2HCl → ZnCl₂ + H₂
B. 2Mg + O₂ → 2MgO
C. NaOH + HCl → NaCl + H₂O
D. C + O₂ → CO

✅ Correct Answer: D. C + O₂ → CO

Explanation: Correct is 2C + O₂ → 2CO.

Q96. Which of the following reactions is used in fire extinguishers?

A. CaCO₃ → CaO + CO₂
B. NaHCO₃ → Na₂CO₃ + CO₂ + H₂O
C. 2KClO₃ → 2KCl + 3O₂
D. NH₄Cl → NH₃ + HCl

✅ Correct Answer: B. NaHCO₃ → Na₂CO₃ + CO₂ + H₂O

Q97. When silver chloride is exposed to sunlight, it decomposes to form:

A. Silver and chlorine gas
B. Silver nitrate and chlorine
C. Silver sulphate
D. Silver hydroxide

✅ Correct Answer: A. Silver and chlorine gas

Q98. The reaction 2H₂ + O₂ → 2H₂O is:

A. Combination reaction
B. Redox reaction
C. Exothermic reaction
D. All of these

✅ Correct Answer: D. All of these

Q99. Which of the following is NOT a chemical change?

A. Rusting of iron
B. Burning of magnesium ribbon
C. Dissolving common salt in water
D. Decomposition of silver bromide

✅ Correct Answer: C. Dissolving common salt in water

Q100. Which is the best explanation for why chemical equations are balanced?

A. To obey Newton’s laws
B. To satisfy conservation of mass
C. To make equations look neat
D. To simplify calculations

✅ Correct Answer: B. To satisfy conservation of mass

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