Iron rusts faster when :

Options

A. exposed to dry air
B. exposed to moist air
C. painted
D. galvanised

Explanation

**Step-by-Step Solution:**

1. **Understanding Rusting**: Rusting is a chemical process where iron reacts with oxygen in the presence of moisture (water) to form rust, which is primarily hydrated ferric oxide (Fe₂O₃·nH₂O).

2. **Conditions for Rusting**: For rusting to occur, two main conditions must be met:
- Presence of oxygen (from the air).
- Presence of moisture (water).

3. **Effect of Moisture**: When iron is exposed to moist air, the water acts as an electrolyte, facilitating the transfer of electrons and speeding up the oxidation process. This means that the more moisture present, the faster the rusting process occurs.

4. **Conclusion**: Therefore, iron rusts faster when it is exposed to moist air rather than dry air. The presence of water vapor in the air increases the rate of rusting.

5. **Final Answer**: Iron rusts faster when exposed to moist air.

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