Master Class 10 Science Chapter 1 — Chemical Reactions and Equations with these 35 carefully
selected NCERT-based MCQs. Every question comes with the correct answer highlighted and a
detailed explanation. Perfect for board exam preparation and quick revision!
📝 Chapter Summary — Chemical Reactions & Equations
Chemical Reactions and Equations is the opening chapter of Class 10 Science.
It introduces students to how substances interact and transform, laying the foundation for all
of Chemistry. The chapter covers writing and balancing equations, types of reactions, and
real-world applications like corrosion and rancidity.
Chemical Reaction: A process in which reactants are converted into products. Observable signs include colour change, gas evolution, precipitate formation, or temperature change.
Balanced Chemical Equation: Based on the Law of Conservation of Mass — the total mass of reactants equals the total mass of products.
Combination Reaction: Two or more substances combine to form a single new substance. Example: CaO + H₂O → Ca(OH)₂ (exothermic).
Decomposition Reaction: A single compound breaks down into two or more simpler substances. Example: CaCO₃ → CaO + CO₂ (requires heat/light/electricity).
Displacement Reaction: A more reactive element displaces a less reactive element from its compound. Example: Fe + CuSO₄ → FeSO₄ + Cu.
Double Displacement Reaction: Ions of two compounds exchange places to form two new compounds, often producing a precipitate. Example: Na₂SO₄ + BaCl₂ → BaSO₄↓ + 2NaCl.
Oxidation and Reduction (Redox): Oxidation = loss of electrons / gain of oxygen. Reduction = gain of electrons / loss of oxygen. They always occur together.
Corrosion: Slow attack of metals by substances in the environment (moisture, oxygen, acids). Example: rusting of iron (Fe₂O₃·xH₂O).
Rancidity: Oxidation of fats and oils in food causes bad smell and taste. Prevented by using antioxidants, inert gas packaging, and refrigeration.
📊 Quick Poll — Share Your Opinion!
Which type of chemical reaction do you find most confusing?
Oxidation and Reduction (Redox)
Double Displacement Reactions
Balancing Chemical Equations
Decomposition Reactions
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❓ 35 MCQs — Chemical Reactions & Equations (NCERT Class 10)
Q1
Which of the following is a physical change?
A Burning of magnesium ribbon
B Rusting of iron
C Melting of ice
D Souring of milk
✓ Correct Answer: C
Solution: Melting of ice is a physical change because no new chemical substance is formed and the process is completely reversible — the water can be refrozen into ice. All other options involve irreversible chemical changes.
Q2
What is the observation when a magnesium ribbon is burnt in air?
A Dazzling white flame
B Yellow flame with soot
C Red hot glow
D Blue flame
✓ Correct Answer: A
Solution: Magnesium burns in air with a characteristic dazzling white flame to form Magnesium Oxide (MgO), a white powdery substance. Equation: 2Mg + O₂ → 2MgO.
Q3
In the reaction: CuO + H₂ → Cu + H₂O, which substance is oxidized?
A CuO
B Cu
C H₂O
D H₂
✓ Correct Answer: D
Solution: Hydrogen (H₂) gains oxygen to form water (H₂O) — this is oxidation. Simultaneously, CuO loses oxygen to form Cu — this is reduction. This is a classic redox reaction.
Q4
The chemical formula of Magnesium Oxide is:
A Mg₂O
B MgO₂
C MgO
D MgOH
✓ Correct Answer: C
Solution: Magnesium has a valency of +2 and Oxygen has a valency of −2. They combine in a 1:1 ratio (cross-multiply method) to give MgO.
Q5
Which gas is evolved when dilute HCl reacts with zinc granules?
A Oxygen
B Hydrogen
C Carbon dioxide
D Nitrogen
✓ Correct Answer: B
Solution: Metals react with dilute acids to produce a salt and hydrogen gas. Zn + 2HCl → ZnCl₂ + H₂↑. The hydrogen gas can be confirmed by the burning splint test (makes a pop sound).
Q6
Balanced chemical equations satisfy which law?
A Law of constant proportions
B Law of conservation of mass
C Law of multiple proportions
D Avogadro's law
✓ Correct Answer: B
Solution: The Law of Conservation of Mass states that mass can neither be created nor destroyed in a chemical reaction. Balancing an equation ensures equal numbers of atoms of each element on both sides.
Q7
Fe₂O₃ + 2Al → Al₂O₃ + 2Fe is an example of a:
A Combination reaction
B Double displacement reaction
C Decomposition reaction
D Displacement reaction
✓ Correct Answer: D
Solution: This is the Thermite reaction. Aluminium is more reactive than iron in the reactivity series, so it displaces iron from its oxide (Fe₂O₃). It is a single displacement (also called a redox) reaction.
Q8
What happens when lead nitrate is heated?
A Evolution of O₂ gas only
B Evolution of NO₂ gas only
C Formation of PbO only
D All of the above
✓ Correct Answer: D
Solution: Thermal decomposition of lead nitrate produces all three: 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂. The brown fumes observed are NO₂ (nitrogen dioxide), and PbO is a yellow solid.
Q9
The reaction: CaO + H₂O → Ca(OH)₂ + Heat is:
A Endothermic
B Exothermic
C Decomposition
D Photolytic
✓ Correct Answer: B
Solution: When quick lime (CaO) reacts with water, it releases a large amount of heat energy, making it an exothermic reaction. It is also a combination reaction since two reactants form one product.
Q10
The formula for Quick Lime is:
A Ca(OH)₂
B CaCO₃
C CaO
D CaCl₂
✓ Correct Answer: C
Solution: Calcium Oxide (CaO) is commonly known as Quick Lime. Ca(OH)₂ is Slaked Lime and CaCO₃ is Limestone (or chalk). These three are frequently asked in board exams.
Q11
What is the colour of the precipitate formed when Barium Chloride reacts with Sodium Sulphate?
A Blue
B Yellow
C White
D Green
✓ Correct Answer: C
Solution: BaCl₂ + Na₂SO₄ → BaSO₄↓ + 2NaCl. Barium Sulphate (BaSO₄) forms a white insoluble precipitate. This is a classic double displacement / precipitation reaction from NCERT.
Q12
Rancidity can be prevented by adding:
A Oxidants
B Antioxidants
C Catalysts
D Bases
✓ Correct Answer: B
Solution: Rancidity is caused by the oxidation of fats and oils. Antioxidants (like BHA, BHT added to chips packets) prevent oxidation. Packaging in nitrogen gas is another common method.
Q13
Which of the following is a decomposition reaction?
A H₂ + O₂ → H₂O
B Zn + CuSO₄ → ZnSO₄ + Cu
C CaCO₃ → CaO + CO₂
D NaOH + HCl → NaCl + H₂O
✓ Correct Answer: C
Solution: In a decomposition reaction, a single compound breaks into two or more simpler substances. CaCO₃ (calcium carbonate / limestone) breaks down on heating into CaO and CO₂. This is a thermal decomposition reaction.
Q14
The brown gas evolved during the thermal decomposition of Lead Nitrate is:
A N₂
B N₂O
C NO₂
D NO
✓ Correct Answer: C
Solution: Nitrogen Dioxide (NO₂) is a reddish-brown coloured gas. It is produced along with PbO and O₂ when lead nitrate is heated: 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂.
Q15
Which of the following gases can be used for storage of a fresh sample of oil for a long time?
A Carbon dioxide or oxygen
B Nitrogen or oxygen
C Carbon dioxide or helium
D Helium or nitrogen
✓ Correct Answer: D
Solution: Inert (unreactive) gases like Nitrogen (N₂) and Helium (He) are used to prevent oxidation of oils. Oxygen would cause rancidity; CO₂ could react with some food components.
Q16
The reaction of lead with a copper chloride solution is a:
A Combination reaction
B Double displacement
C Displacement reaction
D Decomposition
✓ Correct Answer: C
Solution: Pb + CuCl₂ → PbCl₂ + Cu. Lead is higher in the reactivity series than copper, so it displaces copper from its salt solution. This is a single displacement reaction.
Q17
In the reaction: PbO + C → Pb + CO, carbon is acting as a/an:
A Oxidising agent
B Reducing agent
C Catalyst
D Inert substance
✓ Correct Answer: B
Solution: Carbon removes oxygen from Lead Oxide (PbO) and is itself oxidised to CO. The substance that removes oxygen (or causes reduction of another) is called a reducing agent. Here, C reduces PbO.
Q18
The mole ratio of hydrogen and oxygen gases liberated during electrolysis of water is:
A 1 : 1
B 2 : 1
C 4 : 1
D 1 : 2
✓ Correct Answer: B
Solution: 2H₂O → 2H₂ + O₂. From the balanced equation, 2 moles of H₂ are produced for every 1 mole of O₂. The ratio H₂ : O₂ = 2 : 1 (by volume as well, at the same conditions).
Q19
Silver chloride turns grey in sunlight because of the formation of:
A Silver metal
B Chlorine gas
C Silver oxide
D Sublimation of AgCl
✓ Correct Answer: A
Solution: 2AgCl → 2Ag + Cl₂ (in sunlight). This is a photolytic decomposition reaction. The grey colour is due to finely divided silver metal (Ag). This principle was used in old photography.
Q20
Which among the following is a double displacement reaction?
A Pb + CuCl₂ → PbCl₂ + Cu
B Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl
C C + O₂ → CO₂
D CH₄ + 2O₂ → CO₂ + 2H₂O
✓ Correct Answer: B
Solution: In a double displacement reaction, the ions of two ionic compounds exchange places. Na⁺ and Ba²⁺ swap their anions here. Option A is displacement, C is combination, D is combustion.
Q21
What is the common name of Calcium Hydroxide — Ca(OH)₂?
A Quick lime
B Slaked lime
C Limestone
D Bleaching powder
✓ Correct Answer: B
Solution: Ca(OH)₂ = Slaked Lime. CaO = Quick Lime. CaCO₃ = Limestone. Remember: Quick lime + Water → Slaked lime (CaO + H₂O → Ca(OH)₂), a very common reaction in NCERT.
Q22
The reaction between an acid and a base to form salt and water is called:
A Combination
B Redox
C Neutralisation
D Decomposition
✓ Correct Answer: C
Solution: Acid + Base → Salt + Water is a Neutralisation reaction. It is also a type of double displacement reaction. Example: NaOH + HCl → NaCl + H₂O.
Q23
Oxidation involves:
A Addition of oxygen only
B Removal of hydrogen only
C Loss of electrons only
D All of the above
✓ Correct Answer: D
Solution: Oxidation can be defined in three ways: (1) gain of oxygen, (2) loss of hydrogen, or (3) loss of electrons. All three are equivalent definitions of oxidation used at different levels of chemistry.
Q24
When iron nails are dipped in copper sulphate solution, the colour of the solution changes to:
A Blue to colourless
B Blue to light green
C Blue to pink
D Colourless to blue
✓ Correct Answer: B
Solution: Fe + CuSO₄ → FeSO₄ + Cu. Iron displaces copper from its solution. The blue colour of CuSO₄ (due to Cu²⁺ ions) fades and is replaced by the pale green colour of FeSO₄. A reddish-brown deposit of copper also forms on the nail.
Q25
Reduction involves:
A Loss of oxygen only
B Gain of hydrogen only
C Gain of electrons only
D All of the above
✓ Correct Answer: D
Solution: Reduction is defined as: (1) loss of oxygen, (2) gain of hydrogen, or (3) gain of electrons. In CuO + H₂ → Cu + H₂O, CuO is reduced because it loses oxygen.
Q26
Which of the following is an endothermic process?
A Dilution of sulphuric acid
B Condensation of water vapours
C Sublimation of dry ice
D Respiration
✓ Correct Answer: C
Solution: Sublimation of dry ice (solid CO₂ → CO₂ gas) requires the absorption of heat energy from the surroundings — it is endothermic. Dilution of H₂SO₄, condensation, and respiration all release heat (exothermic).
Q27
Barium chloride reacting with ammonium sulphate to form barium sulphate and ammonium chloride is an example of:
A Displacement reaction
B Precipitation reaction
C Combination reaction
D Decomposition reaction
✓ Correct Answer: B
Solution: BaCl₂ + (NH₄)₂SO₄ → BaSO₄↓ + 2NH₄Cl. Barium Sulphate is insoluble and forms a white precipitate. Any double displacement reaction that produces an insoluble precipitate is called a precipitation reaction.
Q28
Identify 'x' and 'y' in the balanced equation: xH₂ + O₂ → yH₂O
A x = 1, y = 1
B x = 2, y = 2
C x = 2, y = 1
D x = 1, y = 2
✓ Correct Answer: B
Solution: 2H₂ + O₂ → 2H₂O. Check: Left side — 4H, 2O. Right side — 4H, 2O. Balanced! So x = 2 and y = 2. This is the combination reaction for formation of water.
Q29
What is the colour of ferrous sulphate crystals?
A White
B Green
C Blue
D Brown
✓ Correct Answer: B
Solution: Ferrous Sulphate (FeSO₄·7H₂O) crystals are pale green in colour. On heating, they lose water, turn white, then decompose further to form Fe₂O₃ (brown/reddish) with the release of SO₂ and SO₃ gases.
Q30
Burning of natural gas is an example of:
A Decomposition reaction
B Exothermic reaction
C Endothermic reaction
D Combination reaction
✓ Correct Answer: B
Solution: CH₄ + 2O₂ → CO₂ + 2H₂O + Heat. Combustion of methane (natural gas) releases significant heat energy, making it exothermic. All combustion reactions are exothermic by definition.
Q31
Respiration is considered an:
A Exothermic reaction
B Endothermic reaction
C Physical change
D Reduction reaction
✓ Correct Answer: A
Solution: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy. Glucose is oxidised during respiration, releasing energy (ATP) used by the body. It is therefore an exothermic (oxidation) reaction.
Q32
Which of the following metals does not corrode easily?
A Iron
B Copper
C Gold
D Silver
✓ Correct Answer: C
Solution: Gold is a noble metal and is highly resistant to chemical attack by oxygen, moisture, and most acids. This is why it remains shiny and tarnish-free, making it valuable in jewellery and electronics.
Q33
Rusting of iron is an example of:
A Reduction
B Decomposition
C Oxidation
D Displacement
✓ Correct Answer: C
Solution: Rusting: 4Fe + 3O₂ + xH₂O → 2Fe₂O₃·xH₂O (hydrated iron oxide). Iron gains oxygen in the presence of moisture — this is oxidation. Rust is reddish-brown hydrated iron(III) oxide.
Q34
A substance added to food containing fats and oils to prevent oxidation is called:
A Preservative
B Antioxidant
C Oxidiser
D Reducing agent
✓ Correct Answer: B
Solution: Antioxidants such as Vitamin C (ascorbic acid) and Vitamin E (tocopherol), as well as synthetic BHA and BHT, are added to food to slow down the oxidation of fats — the main cause of rancidity.
Q35
The representation of a chemical reaction using symbols and formulae is called:
A Chemical change
B Chemical equation
C Chemical property
D Chemical identity
✓ Correct Answer: B
Solution: A chemical equation is a shorthand representation of a chemical reaction using symbols and molecular formulae. A balanced chemical equation also shows the relative quantities of reactants and products.
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All MCQs on this page are based on the NCERT Class 10 Science Chapter 1 — Chemical Reactions and Equations syllabus and are intended solely for educational purposes.
These questions are not a verbatim reproduction of the NCERT textbook. If you spot any error or inaccuracy, please reach out to us.
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