Class 10 Science: Types of Chemical Reactions — Practice Questions with Answers
Exam-style CBSE practice questions on Types of Chemical Reactions (Chemical Reactions and Equations). Try each one first, then reveal the correct answer and a step-by-step explanation. Free, from EduLevel — the AI teacher for CBSE.
Q1medium1 mark
Consider the reaction: 2PbO(s) + C(s) → 2Pb(s) + CO₂(g). Which of the given statements about this reaction are incorrect?
(a) Lead is getting reduced.
(b) Carbon dioxide is getting oxidised.
(c) Carbon is getting oxidised.
(d) Lead oxide is getting reduced.
(a) and (b)
(a) and (c)
(a), (b) and (c)
all
Need a hint?
To determine if a substance is being oxidized or reduced, consider the change in oxidation states of the elements involved in the reaction.
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Answer: (a) and (b)
Explanation: Statement (a) is incorrect because lead oxide (PbO) is reduced to lead (Pb), not lead itself. Statement (b) is incorrect because carbon (C) is oxidized to carbon dioxide (CO₂), not CO₂ itself. Statements (c) and (d) are correct descriptions of the process.
Q2easy1 mark
The reaction Fe₂O₃ + 2Al → Al₂O₃ + 2Fe is an example of which type of reaction?
combination reaction
double displacement reaction
decomposition reaction
displacement reaction
Need a hint?
Consider what happens to the elements involved. Is one element replacing another element in a compound?
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Answer: displacement reaction
Explanation: This is a displacement reaction because the more reactive element, aluminum (Al), displaces the less reactive element, iron (Fe), from its compound, iron(III) oxide (Fe₂O₃).
Q3easy1 mark
What is the result of adding dilute hydrochloric acid to iron filings? Choose the correct outcome.
Hydrogen gas and iron chloride are produced.
Chlorine gas and iron hydroxide are produced.
No reaction takes place.
Iron salt and water are produced.
Need a hint?
Consider the reactivity series of metals and the general reaction between an active metal and an acid.
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Answer: Hydrogen gas and iron chloride are produced.
Explanation: Iron is more reactive than hydrogen, so it displaces hydrogen from hydrochloric acid. The reaction produces iron(II) chloride (a salt) and hydrogen gas.
Q4medium1 markCBSE 2025
Electrolysis of water is a decomposition reaction. What is the mass ratio (MH : MO) of hydrogen gas to oxygen gas liberated at the electrodes during this process?
8:1
2:1
1:2
1:8
Need a hint?
Think about the chemical formula of water and what it tells you about the ratio of hydrogen to oxygen atoms.
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Answer: 1:8
Explanation: The electrolysis of water (2H₂O → 2H₂ + O₂) produces hydrogen and oxygen gas in a 2:1 molar ratio. The mass ratio is calculated as (2 × Molar Mass of H₂) : (1 × Molar Mass of O₂) which is (2 × 2) : (1 × 32) = 4:32, simplifying to 1:8.
Q5medium1 markCBSE 2025
Consider the following three reactions: (i) Dilute hydrochloric acid with sodium hydroxide, (ii) Magnesium oxide with dilute hydrochloric acid, and (iii) Carbon dioxide with sodium hydroxide. What is the common observation in all three cases?
Salt and water are formed
Neutral salts are formed
Hydrogen gas is formed
Acidic salts are formed
Need a hint?
Think about the general types of chemical reactions occurring in each of the given scenarios. What broad category do these reactions fall into?
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Answer: Salt and water are formed
Explanation: All three reactions are examples of neutralization reactions where an acid (or acidic oxide) reacts with a base (or basic oxide) to produce salt and water.
Q6easy1 markCBSE 2025
Identify the main observations from the following list that occur when a magnesium ribbon is burned in air: (i) The ribbon burns with a dazzling white flame. (ii) A white powder is formed. (iii) The magnesium ribbon vaporizes. (iv) An aqueous solution of the white powder turns blue litmus paper red.
(i) and (iv)
(i) and (iii)
(i) and (ii)
(iii) and (iv)
Need a hint?
Think about the characteristic reaction of metals like magnesium when exposed to heat and air. What kind of chemical process is likely occurring?
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Answer: (i) and (ii)
Explanation: When magnesium burns in air, it reacts with oxygen in a combination reaction (2Mg + O₂ → 2MgO), producing a dazzling white flame and forming a white powder of magnesium oxide. Magnesium oxide is a basic oxide, so its aqueous solution would turn red litmus blue, making observation (iv) incorrect.
Q7easy1 markCBSE 2024
From the following list of reactions, identify which are examples of thermal decomposition:
(i) 2AgCl → 2Ag + Cl₂
(ii) CaCO₃ → CaO + CO₂
(iii) 2H₂O → 2H₂ + O₂
(iv) 2KClO₃ → 2KCl + 3O₂
(i) and (ii)
(ii) and (iii)
(iii) and (iv)
(ii) and (iv)
Need a hint?
Thermal decomposition reactions involve the breaking down of a single compound into simpler substances when heated.
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Answer: (ii) and (iv)
Explanation: Thermal decomposition reactions require heat. The decomposition of calcium carbonate (CaCO₃) and potassium chlorate (KClO₃) are initiated by heating. Reaction (i) is photolytic (light) and reaction (iii) is electrolytic (electricity).
Q8medium1 markCBSE 2024
Consider the following statements:
Assertion (A): Decomposition reactions are generally endothermic.
Reason (R): The decomposition of organic matter into compost is an exothermic process.
Which of the following is correct?
Both A and R are true, and R is the correct explanation of A.
Both A and R are true, but R is not the correct explanation of A.
A is true, but R is false.
A is false, but R is true.
Need a hint?
Think about the energy changes involved in breaking chemical bonds versus forming them. Does breaking bonds typically require energy input or release energy?
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Answer: Both A and R are true, but R is not the correct explanation of A.
Explanation: Assertion (A) is true because decomposition reactions require energy (heat, light, or electricity) to break bonds. Reason (R) is also true as composting releases heat. However, R is a specific biological exception and does not explain the general endothermic nature of most decomposition reactions.
Q9easy1 markCBSE 2024
Consider the following statements:
Assertion (A): Silver chloride turns grey when exposed to sunlight.
Reason (R): It undergoes decomposition to form silver and chlorine in the presence of sunlight.
Which of the following is correct?
Both A and R are true and R is the correct explanation of A.
Both A and R are true but R is not the correct explanation of A.
A is true, but R is false.
A is false, but R is true.
Need a hint?
Think about what happens to certain chemical compounds when they are exposed to light energy. This relates to a type of chemical reaction.
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Answer: Both A and R are true and R is the correct explanation of A.
Explanation: Both statements are true. The reason (R) correctly explains the assertion (A) because the decomposition of silver chloride in sunlight produces solid silver, which has a grey color, causing the observed color change.
Q10medium1 markCBSE 2024
Consider the following statements:
Assertion (A): All exothermic reactions are accompanied by the evolution of both heat and light.
Reason (R): Combination reactions can be either exothermic or not.
Which of the following is correct?
Both A and R are true and R is the correct explanation of A.
Both A and R are true but R is not the correct explanation of A.
A is true, but R is false.
A is false, but R is true.
Need a hint?
Think about the definition of exothermic reactions. Do all of them necessarily produce light?
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Answer: A is false, but R is true.
Explanation: Assertion (A) is false because exothermic reactions always evolve heat, but not necessarily light (e.g., neutralization reactions). Reason (R) is true because while most combination reactions are exothermic, not all are, so they 'may or may not be' exothermic.
Q11easy1 markCBSE 2024
From the given options, identify the decomposition reaction where light is the source of energy for the decomposition.
2FeSO₄ → Fe₂O₃ + SO₂ + SO₃
2H₂O → 2H₂ + O₂
2AgBr → 2Ag + Br₂
CaCO₃ → CaO + CO₂
Need a hint?
This question is about a specific type of decomposition reaction. Think about which energy source is mentioned in the question and how it might be represented in a chemical reaction.
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Answer: 2AgBr → 2Ag + Br₂
Explanation: The decomposition of silver bromide (AgBr) into silver and bromine is a photochemical reaction, meaning it is initiated by light energy.
Q12easy1 markCBSE 2024
Which of the following processes involves a combination reaction?
Black and White photography
Burning of coal
Burning of methane
Digestion of food
Need a hint?
Think about what happens when different substances join together to form a new, single substance.
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Answer: Burning of coal
Explanation: The burning of coal (carbon) is a combination reaction where two substances, carbon and oxygen, combine to form a single product, carbon dioxide (C(s) + O₂(g) → CO₂(g)).
Q13medium1 markCBSE 2024
Consider the following potential reactions:
(A) CaSO₄ + Al →
(B) CuSO₄ + Ca →
(C) FeSO₄ + Cu →
(D) ZnSO₄ + Mg →
In which of these cases will new products be formed?
(A) and (B)
(B) and (C)
(C) and (D)
(B) and (D)
Need a hint?
Think about the reactivity series of metals. A more reactive metal can displace a less reactive metal from its salt solution.
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Answer: (B) and (D)
Explanation: A displacement reaction occurs when a more reactive metal displaces a less reactive one. Calcium is more reactive than copper, and magnesium is more reactive than zinc, so reactions will proceed in cases (B) and (D).
Q14medium1 markCBSE 2024
For the reaction 2H₂S + SO₂ → 2H₂O + 3S, which statement is correct?
H₂S is the oxidising agent and SO₂ is the reducing agent.
H₂S is reduced to sulphur.
SO₂ is the oxidising agent and H₂S is the reducing agent.
SO₂ is oxidised to sulphur.
Need a hint?
To determine oxidizing and reducing agents, consider the change in oxidation states of the elements involved in the reaction.
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Answer: SO₂ is the oxidising agent and H₂S is the reducing agent.
Explanation: In this reaction, H₂S loses hydrogen and is oxidized to S, making it the reducing agent. SO₂ loses oxygen and is reduced to S, making it the oxidizing agent.
Q15easy1 markCBSE 2024
Among the following chemical reactions, identify the one that is different from the other three:
(a) NaCl + AgNO₃ → AgCl + NaNO₃
(b) CaO + H₂O → Ca(OH)₂
(c) KNO₃ + H₂SO₄ → KHSO₄ + HNO₃
(d) ZnCl₂ + H₂S → ZnS + 2HCl
NaCl + AgNO₃ → AgCl + NaNO₃
CaO + H₂O → Ca(OH)₂
KNO₃ + H₂SO₄ → KHSO₄ + HNO₃
ZnCl₂ + H₂S → ZnS + 2HCl
Need a hint?
Consider the types of chemical reactions involved. Are they all the same category, like precipitation, combination, or acid-base reactions?
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Answer: CaO + H₂O → Ca(OH)₂
Explanation: Reactions (a), (c), and (d) are double displacement reactions where ions are exchanged. Reaction (b) is a combination reaction where two substances combine to form a single product.
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