Science — CBSE Class 10 board question

(i)

(I) Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions. A large amount of energy is needed to overcome these forces, so they have high melting and boiling points.

(II) Solder is an alloy of lead and tin with a low melting point. This allows it to melt easily and join electrical wires without damaging them due to excessive heat.

(III) Carbon can act as a reducing agent only at very high temperatures. Na and Mg are more reactive than carbon; they are higher in the reactivity series. Hence carbon cannot displace Na or Mg from their oxides — in fact, Na or Mg can reduce carbon dioxide.

---

(ii)

(I) Compound 'X' is Iron(III) oxide (Fe₂O₃).

(II) The reaction is called the Thermite reaction.

(III) Balanced chemical equation:

$$\text{Fe}_2\text{O}_3 (s) + 2\text{Al} (s) \rightarrow \text{Al}_2\text{O}_3 (s) + 2\text{Fe} (l) + \text{Heat}$$

Source: Chemical Reactions and Equations, Chapter 1

---

• For (i)(I): Always mention "strong electrostatic forces" — that phrase earns the mark.
• For (i)(II): The key point is low melting point of solder (not just that it's an alloy).
• For (i)(III): The logic is reactivity series — Na and Mg are above carbon, so carbon cannot reduce their oxides.
• For (ii): The thermite reaction (Fe₂O₃ + Al) is a standard 2-mark question. Examiners expect the correct name "Thermite reaction," correct identification of Fe₂O₃, and a fully balanced equation. Note that Fe is produced in liquid/molten form due to the large heat released — writing (l) is a good addition.