Crystals where dipoles may align themselves in an ordered manner, so that there is a net dipole moment, exhibit

Options

A. Pyro-electricity
B. Piezo-electricity
C. Ferro-electricity
D. Antiferro electricity

Answer

To solve the question regarding the type of crystal in which dipoles align themselves in an ordered manner to produce a net dipole moment, we can analyze the options provided:

### Step-by-Step Solution:

1. **Understanding the Question**:
The question asks about crystals where dipoles align in an ordered manner, resulting in a net dipole moment. We need to identify the correct term that describes this property.

2. **Analyzing the Options**:
- **A. Pyroelectricity**: This property refers to the generation of an electric charge in certain materials when they are heated or cooled. It does not specifically involve the ordered alignment of dipoles to create a net dipole moment.

- **B. PGO Electricity**: This term is often associated with the property of materials where dipoles align in an orderly fashion, leading to the generation of a net dipole moment. This is a key characteristic of this property.

- **C. Ferroelectricity**: This property involves materials that exhibit spontaneous electric polarization, which can be reversed by an external electric field. While it involves dipole alignment, it is more about the polarization rather than just the ordered alignment for a net dipole moment.

- **D. Anti-ferroelectricity**: This is the opposite of ferroelectricity, where dipoles are aligned in opposite directions, leading to a cancellation of the net dipole moment.

3. **Identifying the Correct Answer**:
Based on the analysis:
- Pyroelectricity does not align dipoles in an ordered manner for a net dipole moment.
- Ferroelectricity involves polarization but does not specifically focus on the ordered alignment for a net dipole moment.
- Anti-ferroelectricity results in a decrease of net dipole moment due to opposing dipole alignment.

Therefore, the correct answer is **B. PGO Electricity**, as it specifically describes the ordered alignment of dipoles resulting in a net dipole moment.

### Final Answer:
**B. PGO Electricity**