Here’s the Exercise-wise Question & Answer content for:
📘 Class 10 CBSE Science
Chapter 1: Science Chemical Reactions and Equations
🔍 Exercise-wise Q&A from NCERT Textbook
🔹 In-Text Questions – Page 1
Q1. Why should a magnesium ribbon be cleaned before burning in air?
✅ Answer: Magnesium ribbon is cleaned to remove the oxide layer (magnesium oxide) formed on its surface so that it can burn efficiently in air.
🔹 In-Text Questions – Page 6
Q1. A solution of a substance ‘X’ is used for whitewashing. What is the substance ‘X’? Write its formula and the reaction involved.
✅ Answer:
- Substance ‘X’ is calcium oxide (CaO).
- When it reacts with water, it forms calcium hydroxide which is used for whitewashing.
CaO+H2O→Ca(OH)2CaO + H_2O → Ca(OH)_2
Q2. Why is the amount of gas collected in one of the test tubes in electrolysis of water double that of the other? Name the gas.
✅ Answer:
Water (H₂O) contains two parts hydrogen and one part oxygen. During electrolysis, hydrogen gas is collected in double the amount compared to oxygen.
✅ Hydrogen gas is collected in greater volume.
🔹 Textbook Exercise Questions – Page 13
Q1. Which of the following statements about the reaction is correct?
2Mg+O2→2MgO2Mg + O_2 → 2MgO
(i) Magnesium is oxidized
(ii) Oxygen is reduced
(iii) Magnesium oxide is reduced
(iv) Oxygen is oxidized
✅ Answer: (i) Magnesium is oxidized
Q2. Which of the following is a displacement reaction?
A. NaCl+AgNO3NaCl + AgNO_3
B. Zn+CuSO4→ZnSO4+CuZn + CuSO_4 → ZnSO_4 + Cu
C. H2+Cl2→2HClH_2 + Cl_2 → 2HCl
D. BaCl2+Na2SO4→BaSO4+NaClBaCl_2 + Na_2SO_4 → BaSO_4 + NaCl
✅ Answer: B
Q3. Write a balanced chemical equation for the following reactions:
(a) Hydrogen + Chlorine → Hydrogen chloride
✅ Answer:
H2+Cl2→2HClH_2 + Cl_2 → 2HCl
(b) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
✅ Answer:
3BaCl2+Al2(SO4)3→3BaSO4+2AlCl33BaCl_2 + Al_2(SO_4)_3 → 3BaSO_4 + 2AlCl_3
(c) Sodium + Water → Sodium hydroxide + Hydrogen
✅ Answer:
2Na+2H2O→2NaOH+H22Na + 2H_2O → 2NaOH + H_2
Q4. Write the balanced chemical equations and identify the type of reaction:
(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
✅ Answer:
Ca(OH)2+CO2→CaCO3+H2OCa(OH)_2 + CO_2 → CaCO_3 + H_2O
Type: Combination reaction
(b) Zinc + Hydrochloric acid → Zinc chloride + Hydrogen
✅ Answer:
Zn+2HCl→ZnCl2+H2Zn + 2HCl → ZnCl_2 + H_2
Type: Displacement reaction
(c) Barium chloride + Sodium sulphate → Barium sulphate + Sodium chloride
✅ Answer:
BaCl2+Na2SO4→BaSO4↓+2NaClBaCl_2 + Na_2SO_4 → BaSO_4 ↓ + 2NaCl
Type: Double displacement reaction
(d) Lead nitrate → Lead oxide + Nitrogen dioxide + Oxygen
✅ Answer:
2Pb(NO3)2→2PbO+4NO2+O22Pb(NO_3)_2 → 2PbO + 4NO_2 + O_2
Type: Decomposition reaction