Which of the following does not affect the ionisation potential of the atom ?

Options

A. Nuclear charge
B. electron neutrality with protons
C. penetration effect
D. atomic size.

Answer

To determine which factor does not affect the ionization potential of an atom, we need to analyze the options provided and understand the concept of ionization potential.

### Step-by-Step Solution:

1. **Understanding Ionization Potential:**
- Ionization potential (or ionization energy) is defined as the energy required to remove an electron from the outermost shell of an atom.

2. **Analyzing the Factors:**
- We will evaluate each option to see if it affects the ionization potential.

3. **Option 1: Nuclear Charge**
- Nuclear charge refers to the total charge of the nucleus due to protons. An increase in nuclear charge increases the attraction between the nucleus and the electrons, making it harder to remove an electron. Thus, nuclear charge **does affect** ionization potential.

4. **Option 2: Electron Neutrality with Proton**
- Electron neutrality means that the number of electrons equals the number of protons in an atom. This balance does not influence the energy required to remove an electron from the outermost shell. Therefore, this factor **does not affect** ionization potential and is likely the correct answer.

5. **Option 3: Penetration Effect**
- The penetration effect refers to how close an electron can get to the nucleus based on its orbital type (s, p, d, f). Electrons in s orbitals penetrate closer to the nucleus and experience a stronger attraction, making them harder to remove. Thus, the penetration effect **does affect** ionization potential.

6. **Option 4: Atomic Size**
- Atomic size influences ionization potential inversely. As atomic size increases (down a group), the outer electrons are farther from the nucleus and are easier to remove, leading to lower ionization energy. Conversely, as atomic size decreases (across a period), ionization energy increases. Thus, atomic size **does affect** ionization potential.

7. **Conclusion:**
- The only factor that does not affect the ionization potential of an atom is **electron neutrality with proton**.

### Final Answer:
The factor that does not affect the ionization potential of the atom is **electron neutrality with proton**.

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