Q1
Rusting of iron is an example of a:
Achemical change
Bphysical change
Cneutralisation only
Devaporation
CBSEClass 7 (CBSE)ScienceCh 5 · Topic 2
Chemical Changes
Learning to identify changes where a new substance is formed.
Core concept
Signs that a chemical change has occurred include a colour change, the production of gas (bubbles), the release or absorption of heat, or the formation of a precipitate (an insoluble solid appearing in a solution). Rusting, for example, happens when iron reacts slowly with oxygen and moisture in the air, forming reddish-brown iron oxide — this weakens the metal over time, which is why protective coatings like paint are used to prevent rust.
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• A chemical change forms new substances and is usually not easily reversible.
• Examples: burning paper, rusting of iron, cooking food.
• Signs of chemical change: colour change, gas production, heat change, precipitate formation.
• Rusting occurs when iron reacts with oxygen and moisture over time.