The correct statement regarding F-centre is:

Options

A. Electron are held in the voids of crystals
B. F-centre produces colour to the crystals
C. Conductivity of the crystal increases due to F-centre
D. All of these

Answer

To determine the correct statement regarding F-centres, we need to understand what F-centres are and their significance in solid-state chemistry.

### Step-by-Step Solution:

1. **Definition of F-centres**:
- F-centres are defects in ionic crystals, particularly in alkali halides like NaCl. They are formed when an anion (like Cl-) is missing from the crystal lattice, creating a vacancy. This vacancy can trap an electron, which is responsible for the color and conductivity properties of the crystal.

2. **Formation of F-centres**:
- When NaCl crystals are heated in the presence of sodium vapor, some of the Cl- ions may leave their positions in the lattice, creating vacancies. Electrons from the surrounding lattice can occupy these vacancies, leading to the formation of F-centres.

3. **Properties of F-centres**:
- F-centres are known to impart color to the crystals. The trapped electrons can absorb certain wavelengths of light, leading to the characteristic coloration of the crystals.
- Additionally, the presence of F-centres increases the electrical conductivity of the material. The free electrons can move through the lattice, allowing for the conduction of electricity.

4. **Correct Statement**:
- Among the statements provided, the correct statement regarding F-centres is that "F-centres produce color." This is due to the presence of trapped electrons that can absorb light.

### Conclusion:
The correct statement regarding F-centres is that they produce color in ionic crystals due to the presence of trapped electrons.