Anything that influences the valence electrons will affect the chemistry of the element. Which one of the following factors does not affect the valence shell ?

Options

A. Valence principal quantum number(n)
B. Nuclear charge(Z)
C. Nuclear mass
D. Number of core electrons

Explanation

To solve the question, we need to analyze which of the given factors does not influence the valence shell of an atom. The valence shell is the outermost electron shell of an atom, and the valence electrons are the electrons present in this shell.

### Step-by-Step Solution:

1. **Understanding Valence Electrons**:
- Valence electrons are the electrons in the outermost shell of an atom. They play a crucial role in chemical bonding and reactions.

2. **Identifying the Factors**:
- We need to evaluate the four options provided to determine which one does not affect the valence shell.

3. **Option 1: Valence Principal Quantum Number**:
- The principal quantum number (n) indicates the energy level of an electron in an atom. A change in this number directly affects the valence shell since it defines the shell itself.
- **Conclusion**: This factor does influence the valence shell.

4. **Option 2: Nuclear Charge**:
- Nuclear charge (Z) refers to the total charge of the nucleus due to protons. An increase in nuclear charge pulls electrons closer to the nucleus, affecting the valence electrons and their energy levels.
- **Conclusion**: This factor does influence the valence shell.

5. **Option 3: Nuclear Mass**:
- Nuclear mass is the sum of the number of protons and neutrons in the nucleus. It does not directly affect the valence electrons or their energy levels as it does not influence the electron distribution in the outermost shell.
- **Conclusion**: This factor does NOT influence the valence shell.

6. **Option 4: Number of Core Electrons**:
- Core electrons are the electrons in the inner shells. The presence of core electrons affects the effective nuclear charge experienced by valence electrons, thereby influencing their behavior.
- **Conclusion**: This factor does influence the valence shell.

### Final Answer:
The factor that does not affect the valence shell is **Nuclear Mass**.