Identify the antiferromagnetic substance

Options

A. MnO
B. `Fe_(3)O_(4)`
C. `CrO_(2)`
D. NaCl

Answer

To identify the antiferromagnetic substance from the given options, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Antiferromagnetism**: Antiferromagnetic substances are characterized by the presence of equal numbers of magnetic moments that align in opposite directions. This results in a net magnetic moment of zero.

2. **Analyze the Options**:
- **Option 1: MnO**: Manganese(II) oxide is known to exhibit antiferromagnetic properties due to the arrangement of manganese ions in a crystal lattice.
- **Option 2: Fe3O4**: This is a mixed oxide of iron that exhibits ferrimagnetic properties, not antiferromagnetic.
- **Option 3: CrO2**: Chromium dioxide is a well-known ferromagnetic material.
- **Option 4: NaCl**: Sodium chloride is a typical example of a diamagnetic substance, which does not exhibit any magnetic ordering.

3. **Conclusion**: Based on the analysis, the only substance that fits the criteria for antiferromagnetism is **MnO**.

### Final Answer:
The antiferromagnetic substance is **MnO**.

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