Class 10 · Science · Chapter 1: Chemical Reactions and Equations
Bihar Board · NCERT · CBSE
All 103 objective questions (MCQ) of this chapter — solve first, then tap “Show answer”. Each question shows its source label: «BSEB 2025 · board paper» = verified from the official board paper; «Board-style (practice)» = Study With Me's own practice questions.
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Which of the statements about the reaction below are incorrect?
(a) Lead is getting reduced. (b) Carbon dioxide is getting oxidised. (c) Carbon is getting oxidised. (d) Lead oxide is getting reduced.
Correct answer: (A) (a) and (b)
PbO loses O → PbO is reduced (d is true); C gains O → C is oxidised (c is true). (a) and (b) are incorrect → answer (i).
Fe2O3 + 2Al → Al2O3 + 2Fe — the above reaction is an example of a —
Correct answer: (D) Displacement reaction
The more reactive Al displaces Fe from Fe₂O₃ = displacement (d).
What happens when dilute hydrochloric acid is added to iron filings? Choose the correct answer.
Correct answer: (A) Hydrogen gas and iron chloride are produced.
Fe(s) + 2HCl(aq) → FeCl2(aq) + H2(g) — metal + dilute acid → salt + H₂.
Which of the following pairs represents single displacement reaction?
Correct answer: (D) AgNO3
Copper is more reactive than silver, so it removes silver from AgNO3:
In (A) and (B) copper is less reactive than Na and Mg; in (C) silver is less reactive than iron — so no reaction takes place there.
The decomposition of vegetables and their conversion into compost is an example of which reaction?
Correct answer: (B) Exothermic
When vegetables rot into compost, heat is given out, so it is an exothermic reaction (NCERT Chapter 1 gives this same example). A compost heap feels warm to touch.
Which of the following is not an oxidation reaction?
Correct answer: (D) Precipitation
In combustion and respiration, substances combine with oxygen — these are oxidation. Precipitation (such as the formation of BaSO4) is a double displacement reaction — oxygen is neither added nor removed. So the answer is (D).
Note: digestion of food is mainly the breaking down of large molecules; the digested food (glucose) is oxidised later, in respiration. Among the options, the clearest “not oxidation” answer is precipitation.
Which of the following equations is not balanced?
Correct answer: (D) Pb(NO₃)₂ → PbO + NO₂ + O₂
In (D) there are 2 N and 6 O on the left but 1 N and 5 O on the right — unbalanced. The balanced form:
In the other three equations the atoms of each element are equal on both sides.
Which gas is liberated at the Cathode during electrolysis in water?
Correct answer: (C) Hydrogen
In the electrolysis of water, hydrogen forms at the cathode (negative electrode) and oxygen at the anode (positive electrode). The volume of hydrogen is double that of oxygen (2 : 1).
Which statement is true regarding the reaction given below?
Correct answer: (C) Carbon is being oxidised
Carbon gained oxygen (C → CO), so carbon is oxidised. ZnO lost oxygen (ZnO → Zn), so ZnO is reduced.
Oxidation and reduction are both happening in the same reaction — it is a redox reaction.
Which of the following gases is formed as a result of the reaction of Zinc and dilute hydrochloric acid?
Correct answer: (B) H2
Zinc is more reactive than hydrogen, so it removes hydrogen from the acid (displacement):
Test: a burning splinter brought near it gives a ‘pop’ sound — that is H2 gas.
Which among the following is slaked lime?
Correct answer: (C) Ca(OH)2
Quicklime = CaO. Adding water to it forms slaked lime Ca(OH)2 and gives out a lot of heat:
CaCO3 = limestone / marble.
The chemical name of lime water is-
Correct answer: (B) Calcium hydroxide
Lime water = a clear solution of Ca(OH)2 in water. ‘Slaked lime’ is its common name; its chemical name is calcium hydroxide — so (B).
Quicklime and calcium oxide = CaO — that is not lime water.
Which of the following is a chemical change?
Correct answer: (C) Burning of coal
When coal burns a new substance (CO₂) forms and heat is given out — a chemical change. The others only change state/form.
Rusting of iron is a —
Correct answer: (B) Chemical change
A new substance Fe2O3·xH2O forms — a chemical change.
In a chemical equation, the symbol (aq) means —
Correct answer: (C) Aqueous solution
(aq) = aqueous = dissolved in water.
Which oxide of iron is formed when iron reacts with steam?
Correct answer: (A) Fe3O4
3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g) — steam forms the magnetic oxide of iron Fe3O4. (This is a BSEB model-set question, not from the annual exam.)
What type of reaction is 2Zn + O2 → 2ZnO?
Correct answer: (A) Combination
Two reactants → one product = combination.
What type of reaction is CaCO3(s) heat→ CaO(s) + CO2(g)?
Correct answer: (B) Thermal decomposition
One reactant breaks into two products on heating = thermal decomposition (used to make lime).
When a magnesium ribbon burns in air, it forms —
Correct answer: (B) MgO
It burns with a dazzling white flame and forms a white powder, magnesium oxide.
Why is a magnesium ribbon rubbed with sandpaper before burning?
Correct answer: (B) To remove the oxide layer on it
The MgO layer hinders burning (NCERT in-text question 1).
Which gas is given off when dilute sulphuric acid is poured on zinc granules?
Correct answer: (B) Hydrogen
The colour of the precipitate formed on mixing solutions of lead nitrate and potassium iodide is —
Correct answer: (B) Yellow
Yellow lead iodide (PbI2) forms.
Balancing a chemical equation is based on which law?
Correct answer: (A) Law of conservation of mass
Mass is neither created nor destroyed in a chemical reaction.
On balancing Fe + H2O → Fe3O4 + H2, the coefficients of Fe, H₂O, Fe₃O₄ and H₂ respectively will be —
Correct answer: (B) 3, 4, 1, 4
3Fe + 4H2O → Fe3O4 + 4H2 — Fe: 3 = 3, O: 4 = 4, H: 8 = 8.
The chemical formula of quicklime is —
Correct answer: (C) CaO
CaO = quicklime; Ca(OH)2 = slaked lime.
The chemical name of slaked lime is —
Correct answer: (B) Calcium hydroxide
CaO(s) + H2O(l) → Ca(OH)2(aq) — calcium hydroxide.
The reaction of adding water to quicklime is —
Correct answer: (B) Combination and exothermic
Two substances → one product, and a lot of heat is given out (the beaker becomes hot).
2–3 days after whitewashing, a shiny layer of which substance forms on the wall?
Correct answer: (C) CaCO3
What type of reaction is respiration?
Correct answer: (B) Exothermic
Energy is given out when glucose combines with oxygen.
Which products are formed when crystals of ferrous sulphate are heated?
Correct answer: (B) SO3
2FeSO4(s) heat→ Fe2O3(s) + SO2(g) + SO3(g) — there is a smell of burning sulphur.
The brown fumes given off on heating lead nitrate are of which gas?
Correct answer: (B) NO2
2Pb(NO3)2(s) heat→ 2PbO(s) + 4NO2(g) + O2(g) — the brown gas is NO2.
The ratio of the volumes of hydrogen and oxygen released in the electrolysis of water is —
Correct answer: (C) 2 : 1
2H2O(l) electricity→ 2H2(g) + O2(g) — H₂ : O₂ = 2 : 1.
When white silver chloride is kept in sunlight, its colour becomes —
Correct answer: (B) Grey
2AgCl(s) sunlight→ 2Ag(s) + Cl2(g) — grey because silver forms.
Which type of reaction is used in black-and-white photography?
Correct answer: (B) Decomposition by light
Decomposition of AgBr / AgCl by light.
When barium hydroxide and ammonium chloride are mixed, the test tube —
Correct answer: (B) Becomes cold
This is an endothermic reaction — it takes heat from your palm.
When an iron nail is put in copper sulphate solution, the colour of the solution —
Correct answer: (A) Changes from blue to pale green
FeSO4 (pale green) forms.
Which metal can not displace copper from copper sulphate solution?
Correct answer: (D) Ag
Ag is less reactive than Cu.
Dilute HCl added to iron filings forms —
Correct answer: (B) H2
The white precipitate formed on mixing solutions of sodium sulphate and barium chloride is —
Correct answer: (B) BaSO4
Precipitation reactions produce —
Correct answer: (B) Insoluble salts
NCERT summary: precipitation reactions produce insoluble salts.
What type of reaction is NaOH + HCl → NaCl + H2O?
Correct answer: (C) Double displacement (neutralisation)
Acid + base → salt + water — exchange of ions.
In terms of oxygen, oxidation means —
Correct answer: (B) Gain of oxygen
Oxidation = gain of oxygen or loss of hydrogen.
Reduction is —
Correct answer: (C) Gain of hydrogen
Reduction = loss of oxygen or gain of hydrogen.
In CuO + H2 → Cu + H2O the substance reduced is —
Correct answer: (B) CuO
CuO lost oxygen.
In ZnO + C → Zn + CO the substance oxidised is —
Correct answer: (B) C
C gained oxygen (CO formed).
In MnO2 + 4HCl → MnCl2 + 2H2O + Cl2 the substance oxidised is —
Correct answer: (B) HCl
HCl lost hydrogen to form Cl₂ = oxidation; MnO₂ lost O = reduction.
When copper powder is heated in air, the colour of its surface becomes —
Correct answer: (B) Black
2Cu(s) + O2(g) heat→ 2CuO(s) — black CuO.
The chemical formula of rust is —
Correct answer: (C) Fe2O3·xH2O
Hydrated iron(III) oxide.
Silver articles turning black after some time is called —
Correct answer: (B) Corrosion
Silver turning black is an example of corrosion.
The colour of the layer that forms on copper vessels is —
Correct answer: (B) Green
A green layer on copper — corrosion.
In galvanisation, iron is coated with which metal?
Correct answer: (B) Zinc
Galvanisation = coating with zinc.
Rancidity is caused by —
Correct answer: (B) Oxidation of fats/oils
Oxidation of fats/oils by oxygen in the air.
Which gas is filled in chip packets?
Correct answer: (C) Nitrogen
N₂ is unreactive — it prevents oxidation (going stale).
What do antioxidants prevent in foods?
Correct answer: (B) Oxidation
They prevent the oxidation of fats/oils.
Which of the following is a decomposition reaction?
Correct answer: (B) →
One reactant (H₂O) → two products.
Which of the following is a displacement reaction?
Correct answer: (B) →
The element Zn removed Cu from a compound.
Which of the following is a double displacement reaction?
Correct answer: (C) →
The ions of two compounds were exchanged.
Which of the following is an endothermic reaction?
Correct answer: (A) →
Heat has to be supplied continuously to break down CaCO₃.
Which of the following is not a sign of a chemical reaction?
Correct answer: (D) Only a change in shape (such as folding paper)
Folding paper does not form any new substance.
Burning of natural gas (methane) produces —
Correct answer: (B) H2O
CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) — exothermic.
On balancing C3H8 + O2 → CO2 + H2O, the coefficient of O₂ will be —
Correct answer: (C) 5
C3H8 + 5O2 → 3CO2 + 4H2O — O on the right = 6 + 4 = 10.
Hydrogen and chlorine combine to form HCl — this reaction is —
Correct answer: (A) Combination
Which of the following is an oxidation–reduction (redox) reaction?
Correct answer: (C) →
CuO is reduced (loses O) and H₂ is oxidised (gains O) at the same time.
The correct state symbol for water in the electrolysis of water is —
Correct answer: (B) (l)
Liquid water = (l).
Which of the following is the most reactive metal?
Correct answer: (C) Zn
Reactivity: Zn > Fe > Cu > Ag.
Which gas does sodium metal give when it reacts with water?
Correct answer: (B) Hydrogen
Decomposition of vegetable matter into compost is an example of which type of reaction?
Correct answer: (A) Exothermic
NCERT: formation of compost is an example of an exothermic reaction.
Why is silver chloride stored in dark-coloured bottles?
Correct answer: (B) It decomposes in light
2AgCl(s) sunlight→ 2Ag(s) + Cl2(g) — a dark bottle protects it from light.
Which of the following is a chemical change?
Correct answer: (C) Burning of coal
Coal burns to form CO2 and ash — new substances, so it is chemical. In the other three the substance stays the same.
Why is milk turning into curd a chemical change?
Correct answer: (B) A new substance (lactic acid) forms that cannot turn back into milk
The taste (sour) and texture of curd change because a new substance forms; it cannot be turned back into milk.
The white powder left after burning a Mg ribbon is —
Correct answer: (B) MgO
Mg combines with oxygen in the air to form magnesium oxide (MgO) — a white powder.
Why is a Mg ribbon rubbed with sandpaper before burning?
Correct answer: (B) To remove the layer of MgO on it
The MgO layer stops oxygen from reaching Mg; rubbing removes the layer and the ribbon burns properly.
When solutions of lead nitrate and potassium iodide are mixed, the colour of the precipitate is —
Correct answer: (B) Yellow
Lead iodide (PbI2) is a bright yellow insoluble solid.
How do we test the gas given off when dilute H₂SO₄ is poured on zinc?
Correct answer: (B) A burning splinter brought near it gives a “pop” sound
H₂ burns with a “pop” sound near a burning splinter. Lime water turning milky is the test for CO2.
In a chemical equation, the substances written to the left of the arrow are called —
Correct answer: (B) Reactants
Reactants on the left, products on the right.
What is a skeletal equation?
Correct answer: (B) An unbalanced formula equation
A formula equation in which the number of atoms is not equal on both sides is a skeletal equation.
Balancing a chemical equation is based on which law?
Correct answer: (B) Law of conservation of mass
Conservation of mass: the total mass (and the number of atoms) does not change in a reaction.
How do you correctly write 4 molecules of water?
Correct answer: (C) 4H2O
The coefficient goes in front of the formula: 4H2O. H2O4 would be a completely different substance.
How do you write water in the form of steam in an equation?
Correct answer: (C) (g)
Steam is a gas, so H2O(g) — as in 3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)
In BaCl2(aq) + Na2SO4(aq) → BaSO4 + 2NaCl(aq) the state of BaSO4 will be —
Correct answer: (B) (s)
An insoluble precipitate = solid, so BaSO4(s).
The chemical formula of quicklime is —
Correct answer: (C) CaO
Quicklime = CaO (calcium oxide); slaked lime = Ca(OH)2.
2–3 days after whitewashing, the wall starts to shine because this forms on it —
Correct answer: (B) CaCO3
Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l) — a thin layer of CaCO₃ gives the shine.
Which of the following is an exothermic reaction?
Correct answer: (B) Adding water to quicklime
A lot of heat is released in CaO + water. The other three are decompositions that need energy (endothermic).
The brown fumes given off on heating lead nitrate are of which gas?
Correct answer: (B) NO2
Nitrogen dioxide (NO2) is a brown, poisonous gas; O2 is colourless.
On heating ferrous sulphate crystals, where does the smell of burning sulphur come from?
Correct answer: (B) SO3
2FeSO4(s) heat→ Fe2O3(s) + SO2(g) + SO3(g) — the smell of the oxides of sulphur.
The ratio of the volumes of H₂ and O₂ formed in the electrolysis of water is —
Correct answer: (C) 2 : 1
In H₂O, H : O = 2 : 1, so the volume of H₂ is double that of O₂.
Why does white silver chloride turn grey in sunlight?
Correct answer: (B) It decomposes into silver and chlorine
Decomposition by light: 2AgCl(s) sunlight→ 2Ag(s) + Cl2(g) — the silver formed looks grey.
The test tube becomes cold when barium hydroxide and ammonium chloride are mixed. This reaction is —
Correct answer: (B) Endothermic
Heat was taken from the surroundings (your hand), so it feels cold — endothermic.
What type of reaction is photosynthesis?
Correct answer: (B) Endothermic
Plants absorb the energy of sunlight to make glucose — endothermic.
Which metal can displace copper from copper sulphate solution?
Correct answer: (C) Zinc (Zn)
Zn is more reactive than Cu: Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s). Ag, Au, Pt are less reactive than Cu.
What happens in a double displacement reaction?
Correct answer: (B) Two compounds exchange ions
AB + CD → AD + CB — exchange of ions.
The white precipitate formed on mixing solutions of AgNO3 and NaCl is —
Correct answer: (B) AgCl
AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq) — AgCl is an insoluble white precipitate; NaNO3 stays dissolved.
In CuO + H2 → Cu + H2O which substance is oxidised?
Correct answer: (B) H2
H₂ gained O (formed H₂O) = oxidation; CuO lost O = reduction.
In terms of hydrogen, “oxidation” means —
Correct answer: (B) Loss of hydrogen
Oxidation = gain of O or loss of H (as in HCl → Cl₂).
In 4Na(s) + O2(g) → 2Na2O(s) —
Correct answer: (B) Na is oxidised
Na gained oxygen — Na is oxidised (NCERT in-text question 3(i)).
Rusting of iron requires —
Correct answer: (C) Both oxygen and moisture
Iron does not rust in dry air or in boiled (O₂-free) water — both are needed.
Coating iron with zinc is called —
Correct answer: (B) Galvanisation
Galvanisation (a zinc coating) protects iron from rusting.
The main reason for filling chip packets with nitrogen is —
Correct answer: (B) To prevent rancidity (oxidation)
N₂ removes the oxygen → the oil is not oxidised → the chips do not go stale.
Rancidity is caused by —
Correct answer: (B) Oxidation of fats/oils
Oxidation of fats/oils by oxygen in the air.
Which process takes place in both corrosion and rancidity?
Correct answer: (B) Oxidation
Both are examples of slow oxidation by oxygen in the air.
Case: Riya dipped two clean iron nails in copper sulphate solution for 20 minutes. She saw that the blue colour of the solution faded and a brown coating formed on the nails. What is the correct reason for these observations?
Correct answer: (A) Iron displaced copper from the solution because iron is more reactive than copper
Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s) — the more reactive Fe displaces Cu; the brown coating is copper, and blue CuSO₄ changes to pale green FeSO₄.
Data-based: In an electrolysis-of-water experiment, 24 mL of gas collected in the test tube over the cathode. At the same time, which gas and how much will be in the test tube over the anode?
Correct answer: (A) Oxygen, 12 mL
2H2O(l) → 2H2(g) + O2(g) — H₂ forms at the cathode and O₂ at the anode, in the volume ratio 2 : 1. So 24 mL of H₂ comes with 12 mL of O₂.
Experiment: A student heated green ferrous sulphate crystals in a test tube. Which observation proves that this is a chemical decomposition and not just loss of water?
Correct answer: (B) A sharp smell like burning sulphur and a reddish-brown solid left behind
2FeSO4(s) heat→ Fe2O3(s) + SO2(g) + SO3(g) — the smell of SO₂/SO₃ and the reddish-brown Fe₂O₃ are new substances. Drops of water only show that water of crystallisation was lost.
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