The following is not a function of an impurity present in a crystal:

Options

A. Establishing thermal equilibrium
B. Having tendency to diffuse
C. Contributing to scattering
D. Introducing new electronic energy levels

Answer

To solve the question "The following is not a function of an impurity present in a crystal," we need to analyze the effects of impurities on the properties of a crystal.

### Step-by-Step Solution:

1. **Understanding Impurities in Crystals**:
Impurities are foreign atoms or molecules that are incorporated into the crystal lattice of a solid. They can significantly affect the physical and chemical properties of the crystal.

2. **Functions of Impurities**:
Impurities can influence various properties of a crystal, including:
- **Electrical Conductivity**: Impurities can introduce free charge carriers, affecting conductivity.
- **Melting Point**: The presence of impurities can alter the melting point of a crystal.
- **Thermal Conductivity**: Impurities can disrupt the lattice structure, affecting how heat is conducted.
- **Color**: Certain impurities can impart color to the crystal.

3. **Identifying the Incorrect Function**:
The question asks for a function that is **not** associated with impurities in a crystal. One key aspect that impurities do not influence is the establishment of thermal equilibrium. Thermal equilibrium refers to a state where a system's temperature is uniform and does not change over time. Impurities do not establish thermal equilibrium; rather, they can affect how quickly a crystal reaches thermal equilibrium.

4. **Conclusion**:
Based on the analysis, the correct answer to the question is that establishing thermal equilibrium is **not** a function of an impurity present in a crystal.

### Final Answer:
The following is not a function of an impurity present in a crystal: **Establishing thermal equilibrium**.

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