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 regarding the function of an impurity present in a crystal, we will analyze the options provided and identify which one does not pertain to the functions of impurities in crystals.

### Step 1: Understand the Functions of Impurities
Impurities in crystals can have several functions, including:
1. **Stabilizing Thermal Equilibrium**: This refers to the ability of a material to maintain a steady temperature when in contact with another material. Impurities do not play a significant role in stabilizing thermal equilibrium.
2. **Having Tendency to Diffuse**: Impurities can diffuse within the crystal lattice, moving from one site to another.
3. **Contributing to Scattering**: Impurities can affect how light interacts with the crystal, leading to scattering based on their size and distribution.
4. **Introducing New Energy Levels**: Impurities can create new energy levels within the band structure of the crystal, affecting its electronic properties.

### Step 2: Identify the Incorrect Function
From the functions listed above, we can see that:
- **Stabilizing Thermal Equilibrium** is not a function of an impurity present in a crystal. This is primarily a property of the material itself rather than the impurities.

### Conclusion
The following is not a function of an impurity present in a crystal: **Stabilizing Thermal Equilibrium**.

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