Iron is rendered passive by treatment with

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 "Iron is rendered passive by treatment with?", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Passivation**:
- Passivation is a process where a metal is treated to form a protective oxide layer on its surface. This layer prevents further oxidation and corrosion of the metal.

2. **Identify the Purpose of Passivation**:
- The primary purpose of passivation is to protect the metal (in this case, iron) from environmental factors that could lead to its degradation.

3. **Determine the Chemical Agent for Passivation**:
- To render iron passive, we need to identify a chemical that can effectively form an oxide layer on iron.

4. **Recognize the Common Agents Used for Passivation**:
- Among various chemicals, concentrated nitric acid (HNO3) is well-known for its ability to passivate iron.

5. **Explain the Reaction**:
- When iron is treated with concentrated nitric acid, it reacts to form iron(III) oxide (Fe2O3). This oxide layer acts as a barrier, protecting the underlying metal from further oxidation.

6. **Conclude with the Answer**:
- Therefore, the treatment that renders iron passive is concentrated HNO3.

### Final Answer:
Iron is rendered passive by treatment with concentrated HNO3.

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