📘 Chapter 4 – The World of Metals and Non-metals

🔹 Part 2: Corrosion (Q26–Q50)

Q26. Corrosion of iron is commonly called:

A) Tarnish
B) Rusting
C) Oxidation
D) Burning

✅ Answer: B) Rusting

Explanation:

• (A) Tarnish → Happens on silver.
• (B) Rusting → Corrosion of iron due to air + moisture (Correct).
• (C) Oxidation → General process, not specific.
• (D) Burning → Combustion, not corrosion.

Q27. Which conditions are necessary for rusting?

A) Only oxygen
B) Only water
C) Both oxygen and water
D) Carbon dioxide

✅ Answer: C) Both oxygen and water

Q28. Rust is chemically:

A) Iron sulphide
B) Iron hydroxide
C) Hydrated iron oxide
D) Iron carbonate

✅ Answer: C) Hydrated iron oxide

Q29. Which gas increases rusting when dissolved in water?

A) Oxygen
B) Carbon dioxide
C) Nitrogen
D) Hydrogen

✅ Answer: B) Carbon dioxide

Explanation:
CO₂ makes water slightly acidic, which speeds up rusting.

Q30. Which metal does NOT corrode easily?

A) Iron
B) Copper
C) Aluminium
D) Gold

✅ Answer: D) Gold

Q31. Rusting of iron is an example of:

A) Physical change
B) Chemical change
C) Both physical and chemical change
D) Reversible change

✅ Answer: B) Chemical change

Q32. Which of the following metals forms a protective oxide layer preventing further corrosion?

A) Iron
B) Aluminium
C) Zinc
D) Both B and C

✅ Answer: D) Both B and C

Q33. Rusting causes:

A) Strengthening of iron
B) Weakening of iron
C) No effect
D) Iron becomes shiny

✅ Answer: B) Weakening of iron

Q34. Which method is used to prevent rusting?

A) Oiling
B) Painting
C) Galvanisation
D) All of these

✅ Answer: D) All of these

Q35. Galvanisation is the process of coating iron with:

A) Copper
B) Aluminium
C) Zinc
D) Tin

✅ Answer: C) Zinc

Q36. The greenish deposit on copper vessels is:

A) Copper sulphate
B) Copper carbonate
C) Copper hydroxide + carbonate
D) Copper oxide

✅ Answer: C) Copper hydroxide + carbonate

Q37. Which gas is necessary for corrosion of iron?

A) Nitrogen
B) Oxygen
C) Hydrogen
D) Helium

✅ Answer: B) Oxygen

Q38. Corrosion of silver is called:

A) Rusting
B) Tarnishing
C) Galvanisation
D) Electroplating

✅ Answer: B) Tarnishing

Explanation:
Silver reacts with sulphur compounds in air, forming a black layer of silver sulphide.

Q39. Which process protects iron by coating it with zinc?

A) Electroplating
B) Galvanisation
C) Alloying
D) Painting

✅ Answer: B) Galvanisation

Q40. Stainless steel does not rust because it contains:

A) Iron + Carbon
B) Iron + Nickel + Chromium
C) Iron + Aluminium
D) Iron + Copper

✅ Answer: B) Iron + Nickel + Chromium

Q41. Which is NOT a method of rust prevention?

A) Painting
B) Applying grease
C) Galvanisation
D) Heating iron strongly

✅ Answer: D) Heating iron strongly

Q42. The brown flaky substance formed on iron is:

A) Rust
B) Tarnish
C) Patina
D) Oxide layer of aluminium

✅ Answer: A) Rust

Q43. Which one of these is NOT affected by corrosion?

A) Gold
B) Iron
C) Copper
D) Aluminium

✅ Answer: A) Gold

Q44. The protective green coating on old copper roofs is called:

A) Rust
B) Patina
C) Tarnish
D) Scale

✅ Answer: B) Patina

Q45. The chemical reaction in rusting involves:

A) Only oxygen
B) Only water
C) Oxygen and water
D) Heat

✅ Answer: C) Oxygen and water

Q46. Iron objects last longer when kept in:

A) Moist air
B) Dry air
C) Seawater
D) Rainwater

✅ Answer: B) Dry air

Q47. Which of these metals forms a protective oxide layer naturally?

A) Aluminium
B) Zinc
C) Copper
D) All of these

✅ Answer: D) All of these

Q48. Which is the most corrosion-resistant metal?

A) Silver
B) Gold
C) Iron
D) Zinc

✅ Answer: B) Gold

Q49. Sacrificial protection is related to:

A) Using less iron
B) Coating with paint
C) Using a more reactive metal to protect iron
D) Mixing iron with water

✅ Answer: C) Using a more reactive metal to protect iron

Q50. Which of these metals is protected by forming an oxide layer that sticks tightly?

A) Iron
B) Aluminium
C) Sodium
D) Potassium

✅ Answer: B) Aluminium

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