ScienceCBSE Class 10 · Sample paper, session 2024-25 · 2 marks · Very short answer

CBSE Class 10 Science sample paper 2024-25: question 21

From the official CBSE sample question paper for 2024-25, section B, question 21, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q21 · 2 marks · Very short answerChemical Reactions and Equations

Identify the type of each of the following reactions stating the reason for your answers.
A. $F e_{2} O_{3} + 2Al \to A l_{2} O_{3} + 2Fe + heat$
B. $Pb (N O_{3})_{2} + 2KI \to Pb I_{2} (↓) + 2KN O_{3}$

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2024-25.

Hints

Open one hint at a time and try again before the next.

Hint 1

In A, which element takes the oxygen from which?

Hint 2

In B, look at how the partners swap and what the downward arrow means.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

A. $F e_{2} O_{3} + 2Al \to A l_{2} O_{3} + 2Fe + heat$ is an (exothermic) displacement reaction, which is also a redox reaction.
½ mark
Reason: aluminium is more reactive than iron, so it displaces iron from iron oxide. Al is oxidised and $F e_{2} O_{3}$ is reduced, and heat is released.
½ mark
B. $Pb (N O_{3})_{2} + 2KI \to Pb I_{2} ↓ + 2KN O_{3}$ is a double displacement (precipitation) reaction.
½ mark
Reason: the reactants exchange ions ( $P b^{2 +}$ pairs with $I^{-}$ and $K^{+}$ pairs with $N O_{3}^{-}$ ), and an insoluble yellow precipitate of $Pb I_{2}$ forms.
½ mark

Answer: A: exothermic displacement (redox) reaction; B: double displacement (precipitation) reaction

Where the marks are

Names reaction A as displacement/redox/exothermic (0.5 mark)
Gives the reason: Al, being more reactive, displaces Fe / heat is released (0.5 mark)
Names reaction B as double displacement/precipitation (0.5 mark)
Gives the reason: exchange of ions / yellow PbI₂ precipitate forms (0.5 mark)

Revise the chapter

Chapter: Chemical Reactions and Equations (notes, formulas, where marks are lost and every past question)

Practise this chapterBoard-style questions from Chemical Reactions and Equations, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2024-25: every question, by section.

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CBSE Class 10 Science sample paper 2024-25: question 21

Hints

Step-by-step solution

Revise the chapter

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