Corrosion
Corrosion is the slow damage of a metal by air, moisture, or other substances around it.
In one line: Rust grows where air meets water.
Practice This ConceptUnderstand it
In iron, corrosion commonly appears as rusting. Air supplies oxygen and moisture helps the reaction continue. Because it is slow, students often notice corrosion only after the metal has already started weakening.
Example
Rule to remember
Corrosion of iron needs oxygen from air and water or moisture; both together make rusting faster.
See it worked out
Follow the example line by line, then use the same method on new questions.
Worked example
A wet bicycle left outside develops rust on the chain and frame because oxygen and moisture act on iron.
Method you can reuse
- 1Check whether the metal is exposed to air.
- 2Check whether moisture is present.
- 3If both are present, corrosion risk is high.
Sketch it in your answer
Draw an iron surface with arrows from air and moisture, showing rust forming on the surface.
Check yourself
Answer the question in your head before opening the answer.
Try it yourself
Why does an iron gate rust faster during humid rainy weather?
Think first, then show answerHide answer
Common wrong answer
Saying rusting happens because of moisture alone. That is incomplete because iron also needs oxygen from air.
Don't mix this up
Exam tip
Write it in the exam
Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.
How CBSE asks it
- 1
Enough for 1 mark
Corrosion is the slow damage of a metal by air, moisture, or other substances around it.
- 2
Add for 2 marks
Example: An iron gate left outdoors in rainy weather rusts faster.
- 3
Add for 3 marks
In iron, corrosion commonly appears as rusting.
Practice this concept with focused MCQs
Open the concept quiz intro first, review the test details, and then start a focused MCQ set from this concept only. Instant score and answer review are live now.
Help improve this page
Found something confusing, incorrect, or missing?