Fe is made passive by :

Options

A. dil.`H_(2)SO_(4)`
B. dil. HCl
C. conc.`HNO_(3)`
D. conc.`H_(2)SO_(4)`

Explanation

To solve the question "Fe is made passive by:", we will analyze the options provided and understand the concept of passivation in iron.

### Step-by-Step Solution:

1. **Understanding Passivation**:
- Passivation refers to the process where a metal becomes less reactive due to the formation of a protective layer on its surface. For iron, this usually involves the formation of iron oxides.

2. **Analyzing the Options**:
- The options given are:
- A) Dilute H2SO4
- B) Dilute HCl
- C) Concentrated HNO3
- D) Concentrated H2SO4

3. **Evaluating Each Option**:
- **Dilute H2SO4**: This is not strong enough to cause passivation. It can react with iron but does not form a protective layer.
- **Dilute HCl**: Similar to dilute H2SO4, it does not create a protective oxide layer on iron.
- **Concentrated HNO3**: Concentrated nitric acid is known to oxidize iron and form a layer of iron oxide (Fe2O3) on its surface, which protects the underlying metal from further corrosion.
- **Concentrated H2SO4**: While concentrated sulfuric acid can react with iron, it does not typically lead to the formation of a protective oxide layer like nitric acid does.

4. **Conclusion**:
- Based on the evaluation, the option that effectively makes iron passive by forming a protective layer is **C) Concentrated HNO3**.

### Final Answer:
Fe is made passive by **Concentrated HNO3**.

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