Science (086) — CBSE Class 10 board question

Tube A (Moist Air + Metal M): Metal M will corrode/rust. Both moisture and air (oxygen) are present, which are the two necessary conditions for corrosion.

Tube B (Moist Air + Oil + Metal M): Metal M will not corrode. The layer of oil prevents air (oxygen) from reaching the metal surface, so corrosion does not occur.

Tube C (Dry Air + Drying Agent + Metal M): Metal M will not corrode. The drying agent absorbs all moisture, so only dry air is present. Absence of moisture prevents corrosion.

Conclusion regarding galvanisation: Since metal M is protected by galvanisation, it is iron/steel. Galvanisation involves coating iron with a thin layer of zinc, which prevents contact with moisture and air, thus preventing corrosion even if the coating is slightly damaged.

Source: Chapter 3 – Metals and Non-metals, Section 3.5 Corrosion (Activity 3.14) and Section 3.5.1 Prevention of Corrosion

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• The key concept is that both moisture and oxygen are required simultaneously for corrosion (rusting) to occur.
• In Tube B, oil blocks dissolved air; in Tube C, the drying agent removes moisture — either condition missing stops corrosion.
• The mention of galvanisation is a clue that metal M is iron, since galvanisation specifically protects iron/steel with a zinc coating.
• Examiners expect observations for all three tubes with reasons — never skip any. Award marks are split one per tube.