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 1: Understand Antiferromagnetism
Antiferromagnetic materials are those in which the magnetic moments of atoms or ions align in opposite directions, resulting in a net magnetic moment of zero. This typically occurs in certain metal oxides and transition metal compounds.

### Step 2: Analyze the Given Options
We need to evaluate each option to determine if it is antiferromagnetic. The options provided are:
1. MnO (Manganese(II) oxide)
2. Fe3O4 (Iron(II,III) oxide)
3. (Assuming there are more options, but we will focus on the ones mentioned)

### Step 3: Check the Magnetic Properties of Each Substance
- **MnO**: Manganese(II) oxide is known to exhibit antiferromagnetic behavior due to the alignment of manganese ions in opposite directions.
- **Fe3O4**: Iron(II,III) oxide is a mixed-valence compound that exhibits ferrimagnetism rather than antiferromagnetism. In ferrimagnetic materials, the magnetic moments are unequal and do not cancel out completely, resulting in a net magnetic moment.

### Step 4: Conclusion
From the analysis, we conclude that **MnO** is the antiferromagnetic substance among the options provided.

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

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