On Mulliken scale the average of `IP` and `EA` is known as `"_______"` .

Explanation

To solve the question, we need to understand the concepts of ionization potential (IP) and electron affinity (EA) as they relate to the Mulliken scale.

### Step-by-Step Solution:

1. **Understand the Terms**:
- **Ionization Potential (IP)**: This is the energy required to remove an electron from an atom or ion in its gaseous state.
- **Electron Affinity (EA)**: This is the energy change that occurs when an electron is added to a neutral atom in its gaseous state.

2. **Mulliken Scale**:
- The Mulliken scale is a way to determine the electronegativity of an atom. It is based on the average of the ionization potential and electron affinity.

3. **Formula**:
- According to the Mulliken scale, the electronegativity (χ) of an atom can be calculated using the formula:
\[ \chi = \frac{IP + EA}{2} \]
- This means that the electronegativity is the average of the ionization potential and electron affinity.

4. **Conclusion**:
- Therefore, on the Mulliken scale, the average of IP and EA is known as the **"electronegativity of an atom."**

### Final Answer:
On the Mulliken scale, the average of IP and EA is known as **"electronegativity of an atom."**

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