CBSE Class 10 Chemistry Chemical Reactions and Equations MCQs Set 40

Chemistry Objective Questions and Answers: Chemical Reactions and Equations

Access targeted multiple-choice questions for Chemical Reactions and Equations designed to align with the latest CBSE academic syllabus for Class 10 Chemistry. These objective practice sets help students evaluate their conceptual understanding and improve exam readiness.

Download Chemical Reactions and Equations MCQs with Answers

Access the complete set of multiple-choice questions for Chemical Reactions and Equations below. This focused format allows students to isolate specific topics for thorough review and uninterrupted practice alongside official CBSE textbooks.

Multiple Choice Questions

Question 1: The reaction H2 + Cl2 → 2HCl is
(a) an oxidation reaction only
(b) a reduction reaction only
(c) a combination reaction
(d) an isomerisation reaction
Show Answer & Explanation

Answer: (c) a combination reaction

Explanation:
1. Two elements combine to form a single compound.
2. That makes it a combination reaction (it is also a redox reaction).

Teacher's Note:
1. Combination: A + B → AB.
2. Isomerisation is rearrangement of atoms within a molecule.

Question 2: Which one of the following is used for the white washing of walls?
(a) calcium oxide mixed with water
(b) calcium carbonate mixed with water
(c) calcium sulphate mixed with water
(d) sodium chloride mixed with water
Show Answer & Explanation

Answer: (a) calcium oxide mixed with water

Explanation:
1. Quick lime reacts with water to give slaked lime: CaO + H2O → Ca(OH)2.
2. The slaked lime solution is applied to walls and slowly forms a shiny white coat of calcium carbonate.

Teacher's Note:
1. Ca(OH)2 + CO2 → CaCO3 + H2O.
2. The reaction is exothermic.

Question 3: Copper displaces which of the following metals from its salt solution?
(a) ZnSO4
(b) FeSO4
(c) AgNO3
(d) NiSO4
Show Answer & Explanation

Answer: (c) AgNO3

Explanation:
1. Copper is less reactive than zinc, iron and nickel but more reactive than silver.
2. So it displaces silver from AgNO3, and the solution turns blue.

Teacher's Note:
1. Reactivity order: Zn > Fe > Ni > Cu > Ag.
2. A metal displaces only metals below it.

Question 4: Match the oxidation states of the underlined elements: (A) Xe in XeF4, (B) N in NH4+, (C) Xe in XeO2F2, (D) P in Na3PO4 with (P) –3, (Q) +4, (R) +5, (S) +6.
(a) A-Q, B-P, C-S, D-R
(b) A-P, B-Q, C-R, D-S
(c) A-S, B-R, C-Q, D-P
(d) A-R, B-S, C-P, D-Q
Show Answer & Explanation

Answer: (a) A-Q, B-P, C-S, D-R

Explanation:
1. XeF4: Xe + 4(–1) = 0 so Xe = +4. NH4+: N + 4(+1) = +1 so N = –3.
2. XeO2F2: Xe + 2(–2) + 2(–1) = 0 so Xe = +6. Na3PO4: 3(+1) + P + 4(–2) = 0 so P = +5.
3. So A-Q, B-P, C-S, D-R.

Teacher's Note:
1. Write the algebraic sum of oxidation numbers equal to the charge.
2. F is always –1 in compounds.

Question 5: A substance which oxidises itself and reduces others is known as a
(a) oxidising agent
(b) reducing agent
(c) both of these
(d) none of these
Show Answer & Explanation

Answer: (b) reducing agent

Explanation:
1. A reducing agent gives electrons and is oxidised itself while it reduces another substance.
2. So the answer is reducing agent.

Teacher's Note:
1. Oxidising agent: gets reduced, oxidises others.
2. Reducing agent: gets oxidised, reduces others.

Question 6: In the reaction P4 → H2PO2– + PH3 in alkaline medium, which statement is correct?
(a) P4 is both oxidised and reduced (disproportionation)
(b) P4 is only oxidised
(c) P4 is only reduced
(d) it is not a redox reaction
Show Answer & Explanation

Answer: (a) P4 is both oxidised and reduced (disproportionation)

Explanation:
1. Phosphorus changes from 0 in P4 to +1 in H2PO2– (oxidation) and to –3 in PH3 (reduction).
2. One species is both oxidised and reduced, so it is a disproportionation reaction.

Teacher's Note:
1. In disproportionation the same substance acts as oxidising and reducing agent.
2. Both oxidation number changes must be present.

Question 7: Which of the following equations is NOT balanced? (i) Fe + Cl2 → FeCl3 (ii) Mg + CuSO4 → MgSO4 + Cu (iii) NaOH + HCl → NaCl + H2O (iv) N2O3 → N2 + 3O2
(a) (i) and (iv)
(b) (ii) and (iii)
(c) (i) and (ii)
(d) (iii) and (iv)
Show Answer & Explanation

Answer: (a) (i) and (iv)

Explanation:
1. (i) has 1 Cl2 (2 Cl atoms) on the left and 3 Cl atoms on the right, so it is not balanced.
2. (iv) has 3 oxygen atoms on the left but 6 on the right, so it is not balanced.
3. (ii) and (iii) are balanced.

Teacher's Note:
1. Count atoms of each element on both sides.
2. N2O3 gives N2 + 3/2 O2, or 2N2O3 → 2N2 + 3O2.

Question 8: The oxidation number of carbon in formaldehyde, CH2O, is
(a) 0
(b) +2
(c) –2
(d) +4
Show Answer & Explanation

Answer: (a) 0

Explanation:
1. H is +1 and O is –2, so x + 2(1) + (–2) = 0.
2. So x = 0.

Teacher's Note:
1. The oxidation number of C varies from –4 in CH4 to +4 in CO2.
2. Methanol –2, formaldehyde 0, formic acid +2.

Question 9: Which of the following is the correct balanced equation for Cr2O72– + SO2 → Cr3+ + SO42– in acidic medium?
(a) Cr2O72– + 3SO2 + 2H+ → 2Cr3+ + 3SO42– + H2O
(b) 2Cr2O72– + 3SO2 + 2H+ → 2Cr3+ + SO42– + H2O
(c) Cr2O72– + 3SO2 → 2Cr3+ + 3SO42–
(d) Cr2O72– + SO2 + H+ → Cr3+ + SO42– + H2O
Show Answer & Explanation

Answer: (a) Cr2O72– + 3SO2 + 2H+ → 2Cr3+ + 3SO42– + H2O

Explanation:
1. Cr changes from +6 to +3 (3 electrons each, 6 for Cr2O72–) and S from +4 to +6 (2 electrons each).
2. So 3 SO2 are needed for each Cr2O72–.
3. Balancing O and charge with H+ and H2O gives the first equation (charge 0 on both sides).

Teacher's Note:
1. The total electrons lost must equal the total electrons gained.
2. Check O, H and charge at the end.

Question 10: Hydrogen sulphide is a strong reducing agent. In which of the following reactions does it show its reducing action?
(a) CuSO4 + H2S → CuS + H2SO4
(b) Pb(NO3)2 + H2S → PbS + 2HNO3
(c) Cd(NO3)2 + H2S → CdS + 2HNO3
(d) 2FeCl3 + H2S → 2FeCl2 + 2HCl + S
Show Answer & Explanation

Answer: (d) 2FeCl3 + H2S → 2FeCl2 + 2HCl + S

Explanation:
1. In (a) Fe goes from +3 to +2 (reduced) and S goes from –2 to 0 (oxidised), so H2S acts as the reducing agent.
2. The other three reactions are precipitations of sulphides with no change in oxidation numbers.

Teacher's Note:
1. Reducing action means the oxidation number of S increases.
2. Metal sulphides precipitate without redox.

Question 11: In the reaction C2H5OH + O2 → CO2 + H2O (unbalanced), which statements are correct?
(a) Carbon is oxidised and oxygen is reduced
(b) Carbon is reduced and oxygen is oxidised
(c) Carbon acts as the oxidising agent
(d) both carbon and oxygen are oxidised
Show Answer & Explanation

Answer: (a) Carbon is oxidised and oxygen is reduced

Explanation:
1. Carbon goes from –2 (average in ethanol) to +4 in CO2, so it is oxidised.
2. Oxygen goes from 0 to –2, so it is reduced and acts as the oxidising agent.

Teacher's Note:
1. Combustion is oxidation of the fuel.
2. Oxygen is the oxidising agent.

Question 12: What mass of quick lime (CaO) can be obtained by heating 200 kg of limestone that is 95% pure?
(a) 601.4 kg
(b) 112 kg
(c) 160.4 kg
(d) 106.4 kg
Show Answer & Explanation

Answer: (d) 106.4 kg

Explanation:
1. Pure CaCO3 = 0.95 × 200 = 190 kg.
2. CaCO3 → CaO + CO2: 100 g gives 56 g, so 190 kg gives 190 × 56 / 100 = 106.4 kg.

Teacher's Note:
1. Always remove the impurity first.
2. The mole ratio CaCO3 : CaO is 1 : 1.

Question 13: Which of the following correctly matches the type of reaction with the example? (A) double displacement (B) decomposition (C) precipitation (D) redox. Examples: (P) CuO + H2 → Cu + H2O, (Q) Na2SO4 + BaCl2 → BaSO4↓ + 2NaCl, (R) CaCO3 → CaO + CO2, (S) NaOH + HCl → NaCl + H2O
(a) A-P; B-Q; C-R; D-S
(b) A-S; B-P; C-Q; D-R
(c) A-R; B-S; C-P; D-Q
(d) A-Q,S; B-R; C-Q; D-P
Show Answer & Explanation

Answer: (d) A-Q,S; B-R; C-Q; D-P

Explanation:
1. Q and S both exchange ions, so both are double displacement.
2. R is thermal decomposition and Q forms an insoluble precipitate of BaSO4.
3. P involves transfer of oxygen and hydrogen (oxidation and reduction), so it is redox.

Teacher's Note:
1. A reaction can belong to more than one category.
2. Precipitation is a special double displacement.

Question 14: In the electrolysis of water, the volume ratio of hydrogen to oxygen collected is
(a) 3 : 1
(b) 2 : 1
(c) 1 : 2
(d) 1 : 1
Show Answer & Explanation

Answer: (b) 2 : 1

Explanation:
1. 2H2O → 2H2 + O2: two moles (volumes) of hydrogen are produced for each mole of oxygen.
2. So the ratio of H2 to O2 is 2 : 1.

Teacher's Note:
1. The test tube at the cathode has double the gas.
2. Hydrogen burns with a pop sound, oxygen relights a glowing splinter.

Question 15: Among Al, K, Ca and Au, the most reactive and the least reactive metals are respectively
(a) Au and K
(b) Al and Ca
(c) K and Au
(d) Ca and Al
Show Answer & Explanation

Answer: (c) K and Au

Explanation:
1. In the reactivity series the order is K > Ca > Al > ... > Au.
2. So potassium is the most reactive and gold the least reactive.

Teacher's Note:
1. Reactivity series (high to low): K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Ag, Au.
2. Metals above hydrogen displace it from dilute acids.

Question 16: In the reaction MnO2 + 4HCl → MnCl2 + 2H2O + Cl2, the oxidising agent and the reducing agent are respectively
(a) MnO2 and MnCl2
(b) Cl2 and HCl
(c) MnO2 and HCl
(d) HCl and MnO2
Show Answer & Explanation

Answer: (c) MnO2 and HCl

Explanation:
1. Mn goes from +4 to +2, so MnO2 is reduced and is the oxidising agent.
2. Cl goes from –1 in HCl to 0 in Cl2, so HCl is oxidised and is the reducing agent.

Teacher's Note:
1. The oxidising agent is the substance reduced.
2. Only 2 of the 4 HCl are oxidised.

Question 17: A, B and C are elements with the reactions A2O3 + 2B → B2O3 + 2A, 3CSO4 + 2B → B2(SO4)3 + 3C and 3CO + 2A → A2O3 + 3C. The most reactive and the least reactive elements are respectively
(a) B and C
(b) B and A
(c) A and C
(d) C and B
Show Answer & Explanation

Answer: (a) B and C

Explanation:
1. In the first reaction B displaces A, so B > A.
2. In the second B displaces C, so B > C.
3. In the third A displaces C, so A > C.
4. The order is B > A > C: B is the most reactive and C the least.

Teacher's Note:
1. A more reactive element displaces a less reactive one.
2. Arrange all the pairs in a single order.

Question 18: The equation CaCO3(s) → CaO(s) + CO2(g) on heating conveys that (Ca = 40, C = 12, O = 16)
(a) 1 g of CaCO3 gives 1 g of each product
(b) 100 g of CaCO3 gives 100 g of CaO
(c) 56 g of CaCO3 gives 100 g of CaO
(d) 100 g of CaCO3 gives 56 g of CaO and 44 g of CO2
Show Answer & Explanation

Answer: (d) 100 g of CaCO3 gives 56 g of CaO and 44 g of CO2

Explanation:
1. Molar masses: CaCO3 = 100, CaO = 56 and CO2 = 44 g mol–1.
2. So 100 g of CaCO3 gives 56 g of CaO and 44 g of CO2 (22.4 L at NTP), and mass is conserved (56 + 44 = 100).

Teacher's Note:
1. A balanced equation tells the mole, mass and gas-volume ratios.
2. It does not tell the speed of the reaction.

Question 19: The colour of copper sulphate solution changes when an iron nail is dipped in it because
(a) water is formed
(b) iron displaces copper, forming pale green iron(II) sulphate
(c) iron turns blue
(d) copper is oxidised to a black oxide
Show Answer & Explanation

Answer: (b) iron displaces copper, forming pale green iron(II) sulphate

Explanation:
1. Fe + CuSO4 → FeSO4 + Cu.
2. The blue colour of CuSO4 fades to the pale green colour of FeSO4, and brown copper is deposited on the nail.

Teacher's Note:
1. Iron is more reactive than copper.
2. Both the nail and the solution change colour.

Question 20: The reaction between iron and copper sulphate solution and the reaction between sodium sulphate and barium chloride solutions are respectively
(a) displacement and double displacement
(b) decomposition and combination
(c) double displacement and displacement
(d) combination and decomposition
Show Answer & Explanation

Answer: (a) displacement and double displacement

Explanation:
1. Iron displaces copper from CuSO4, so it is a displacement reaction.
2. Na2SO4 + BaCl2 exchange ions to give BaSO4 and NaCl, so it is a double displacement reaction.

Teacher's Note:
1. In displacement one element replaces another.
2. In double displacement two compounds exchange ions.

Question 21: What is the sum of all the coefficients when the equation Fe2O3 + CO → Fe + CO2 is balanced using the smallest whole numbers?
(a) 8
(b) 10
(c) 7
(d) 9
Show Answer & Explanation

Answer: (d) 9

Explanation:
1. Balance the atoms of each element in turn.
2. The balanced equation is Fe2O3 + 3CO → 2Fe + 3CO2.
3. The coefficients add up to 1+3+2+3 = 9.

Teacher's Note:
1. Never change a subscript while balancing, only the coefficients.
2. Check every element on both sides at the end.

Question 22: What is the sum of all the coefficients when the equation KI + H2O2 → KOH + I2 is balanced using the smallest whole numbers?
(a) 6
(b) 8
(c) 4
(d) 5
Show Answer & Explanation

Answer: (a) 6

Explanation:
1. Balance the atoms of each element in turn.
2. The balanced equation is 2KI + H2O2 → 2KOH + I2.
3. The coefficients add up to 2+1+2+1 = 6.

Teacher's Note:
1. Never change a subscript while balancing, only the coefficients.
2. Check every element on both sides at the end.

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