Q1.
You would have often noticed that iron objects develop brown deposits when left in the open for a few days. In which conditions would an iron object develop brown deposits? ❖ When it comes into contact with dry air only. ❖ When it comes into contact with water only. ❖ When it comes into contact with both air and water.
Answer
The correct condition is the third one — when it comes into contact with both air and water.
Dry air only → no brown deposit
Water only (no dissolved air) → no brown deposit
Air and water together → brown deposit forms
Water only (no dissolved air) → no brown deposit
Air and water together → brown deposit forms
Do not accept this as a guess — Activity 4.5 sets up exactly these three conditions in three bottles and lets you see the answer for yourself over 8 – 10 days.
Check it yourself: look at an iron gate in your locality. The worst rusting is always at the bottom edge, where rainwater collects and air is still available — not on a dry sheltered part.