Lesson note
NCERT Chapter Exercises and Revision
How to use this lesson
Attempt every question on paper first. Reveal the answer only after writing your own. For equations, check formulae, coefficients, physical states and conditions separately.
Study questions
Questions and answers
Question 1
Which of the statements about the reaction below are incorrect? 2PbO(s) + C(s) → 2Pb(s) + CO₂(g) (a) Lead is getting reduced. (b) Carbon dioxide is getting oxidised. (c) Carbon is getting oxidised. (d) Lead oxide is getting reduced. (i) (a) and (b) (ii) (a) and (c) (iii) (a), (b) and (c) (iv) all
Try first, then reveal the answer
(i) (a) and (b). Lead oxide loses oxygen and is reduced to lead. Carbon gains oxygen and is oxidised to carbon dioxide. Therefore, statements (c) and (d) are correct.
Question 2
Fe₂O₃ + 2Al → Al₂O₃ + 2Fe The above reaction is an example of a (a) combination reaction. (b) double displacement reaction. (c) decomposition reaction. (d) displacement reaction.
Try first, then reveal the answer
(d) Displacement reaction. Aluminium is more reactive than iron and displaces iron from iron oxide.
Question 3
What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer. (a) Hydrogen gas and iron chloride are produced. (b) Chlorine gas and iron hydroxide are produced. (c) No reaction takes place. (d) Iron salt and water are produced.
Try first, then reveal the answer
(a) Hydrogen gas and iron chloride are produced.
Fe(s) + 2HCl(aq) → FeCl₂(aq) + H₂(g)Question 4
What is a balanced chemical equation? Why should chemical equations be balanced?
Try first, then reveal the answer
A balanced chemical equation has the same number of atoms of every element on the reactant and product sides. Equations must be balanced to obey the law of conservation of mass: mass can neither be created nor destroyed during a chemical reaction.
Group Activity
- Take four beakers and label them A, B, C and D.
- Put 25 mL water in A, B and C, and copper sulphate solution in D.
- Measure and record the temperature of every liquid.
- Add two spatulas of potassium sulphate, ammonium nitrate, anhydrous copper sulphate and fine iron filings to A, B, C and D respectively. Stir each mixture.
- Measure and record the final temperature.
- Use the temperature changes to decide which processes are exothermic and which are endothermic.
Safety: Perform the activity under teacher supervision and avoid direct contact with the chemicals.
Common mistakes
- Omitting physical states when the question gives them.
- Naming a reaction without explaining the reactant-product pattern.
- Giving only one example when a question asks for two.
- Forgetting to write heat, light or electricity over the arrow.
Board tips
- Underline the final balanced equation after checking atoms.
- In reasoning answers, write cause → process → observation.
- For redox, name both substances and the oxygen change.
- For multi-part questions, label every subpart exactly.
Revision ladder
- Write correct formulae. 2. Balance coefficients. 3. Add states. 4. Add conditions. 5. Identify the pattern. 6. State the observation or reason.
One-minute revision
- Balance by coefficients, never by changing formulae.
- Conditions are part of a complete equation.
- Activity observations often identify the reaction type.
- Full-mark answers explain why, not only what.
End-of-lesson comic recap
Comic recap
Quick scene, quick smile, quick memory. Read this once and the idea sticks better.