What are the harmful effects of corrosion ? Mention a type of corrosion which is helpful to the metal.

Explanation

**Step-by-Step Solution:**

1. **Understanding Corrosion:**
- Corrosion is the process where metals deteriorate due to chemical reactions with their environment. This often results in the formation of oxides, hydroxides, or other compounds.

2. **Harmful Effects of Corrosion:**
- **Reduction in Strength:** For example, rusting of iron occurs when it reacts with moist air (which contains water vapor). This leads to the formation of rust (iron oxide), which is brittle and reduces the strength of the iron.
- **Increased Risk of Accidents:** The weakened structure of corroded metals can lead to failures in buildings, bridges, and other infrastructures, posing safety hazards.
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