question answer 3

 Certainly, Mayank. Here's a well-structured, CBSE-exam–oriented answer for all three questions, suitable for Class 10 Science students:

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Q1. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

✅ Answer:

When an iron nail is dipped in copper sulphate (CuSO₄) solution, a displacement reaction occurs. Iron is more reactive than copper and displaces copper from its solution:

$$\text{Fe} (s) + \text{CuSO}_4 (aq) \rightarrow \text{FeSO}_4 (aq) + \text{Cu} (s)$$

• The blue colour of the copper sulphate solution fades as iron sulphate (FeSO₄) is formed (which is pale green in colour).

• A reddish-brown deposit of copper forms on the iron nail.

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Q2. Give an example of a double displacement reaction other than the one in Activity 1.10.

✅ Answer:

Reaction between lead(II) nitrate and potassium iodide:

$$\text{Pb(NO}_3)_2 (aq) + 2\text{KI} (aq) \rightarrow \text{PbI}_2 (s) + 2\text{KNO}_3 (aq)$$

• Lead iodide (PbI₂) is a yellow precipitate.

• This is a double displacement and precipitation reaction because the ions exchange to form a new insoluble product.

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Q3. Identify the substances that are oxidised and the substances that are reduced in the following reactions:

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(i) $4\text{Na}(s) + \text{O}_2(g) \rightarrow 2\text{Na}_2\text{O}(s)$

• Sodium (Na) is oxidised (gains oxygen to form Na₂O).

• Oxygen (O₂) is reduced (is combined with sodium).

✅ Oxidised: Sodium (Na)
✅ Reduced: Oxygen (O₂)

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(ii) $\text{CuO}(s) + \text{H}_2(g) \rightarrow \text{Cu}(s) + \text{H}_2\text{O}(l)$

• Copper oxide (CuO) is reduced (loses oxygen to become copper).

• Hydrogen (H₂) is oxidised (gains oxygen to form water).

✅ Oxidised: Hydrogen (H₂)
✅ Reduced: Copper oxide (CuO)

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✅ Tip for Students:

To identify:

• Oxidation: Look for gain of oxygen / loss of hydrogen

• Reduction: Look for loss of oxygen / gain of hydrogen

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Let me know if you'd like a worksheet or MCQ quiz based on this topic!