The lattice site in a pure crystal cannot be occupied by :

Options

A. molecule
B. ion
C. electron
D. atom

Explanation

To solve the question "The lattice site in a pure crystal cannot be occupied by:", we will analyze the types of particles that can occupy lattice sites in a pure crystal and determine which one cannot.

### Step-by-Step Solution:

1. **Understanding Lattice Sites**:
- In a pure crystal, the lattice sites are the specific positions in the crystal structure where the constituent particles (atoms, ions, or molecules) are arranged in a regular pattern.

2. **Identifying Constituents of a Pure Crystal**:
- A pure crystal is made up of a single type of constituent, which can be atoms (like in metals), ions (like in ionic compounds), or molecules (like in molecular solids).
- These constituents occupy the lattice points in a fixed stoichiometric ratio.

3. **Considering Electrons**:
- Electrons are not considered as constituents of a pure crystal. They are subatomic particles that can move freely in certain conditions, especially in conductive materials.
- In a perfect crystal lattice, electrons do not occupy lattice sites; they are typically associated with the bonds between atoms or ions.

4. **Conclusion**:
- Therefore, in a pure crystal, the lattice sites cannot be occupied by electrons. They can only occupy lattice sites in cases of imperfections or defects in the crystal structure.

5. **Final Answer**:
- The correct answer is that lattice sites in a pure crystal cannot be occupied by **electrons**.