Which of the following statement is correct here

Options

A. `AgBr` can show both Schottky and Frenkel defects
B. `ZnO` on heating shows metal excess defects
C. `MnO_2` is ferromagnetic substance
D. Both A and B are correct

Answer

To solve the question about which statements regarding defects in crystals are correct, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Understanding Schottky and Frenkel Defects**:
- **Schottky Defect**: This defect occurs when an equal number of cations and anions are missing from the crystal lattice. In the case of AgBr, when Ag+ ions and Br- ions are missing in equal amounts, it results in a Schottky defect. This leads to a decrease in density.
- **Frenkel Defect**: This defect occurs when an ion (typically a cation) moves to an interstitial site, creating a vacancy in its original position. The overall density of the crystal remains unchanged because the number of ions is conserved.

**Conclusion**: AgBr can exhibit both Schottky and Frenkel defects. Therefore, the first statement is **true**.

2. **Analyzing ZnO and Metal Excess**:
- When ZnO is heated, it can exhibit a metal excess defect. In this case, some Zn2+ ions occupy interstitial sites, and to maintain charge neutrality, electrons are introduced into the lattice. This results in a defect where there are more cations than anions, leading to a metal excess condition.
- Additionally, this defect can impart a yellow color to the ZnO crystals.

**Conclusion**: The statement regarding ZnO showing metal excess on heating is **true**.

3. **Determining the Magnetic Nature of MnO2**:
- MnO2 is known to be an anti-ferromagnetic substance. This means that it has paired electrons, resulting in zero unpaired electrons. Consequently, the overall dipole moment is zero, indicating that it is not paramagnetic.
- Since MnO2 has no unpaired electrons, it does not exhibit paramagnetism.

**Conclusion**: The statement claiming that MnO2 is a paramagnetic substance is **false**.

### Final Answers:
- The first statement about AgBr showing both Schottky and Frenkel defects is **true**.
- The second statement about ZnO being a metal excess on heating is **true**.
- The third statement about MnO2 being a paramagnetic substance is **false**.