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

Answer

To solve the question regarding which factor does not affect the valence shell of an element, we will analyze each option provided.

### 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 determining the chemical properties and reactivity of the element.

2. **Evaluating the Options**:
- **Option 1: Principal Quantum Number (n)**
- The principal quantum number (n) indicates the energy level of the electron shell. Changing n changes the shell number, which directly affects the valence shell. Thus, this option does affect the valence shell.

- **Option 2: Nuclear Charge**
- Nuclear charge refers to the total charge of the nucleus, which is determined by the number of protons. An increase in nuclear charge affects the attraction between the nucleus and the valence electrons, influencing their energy and stability. Therefore, this option also affects the valence shell.

- **Option 3: Mass**
- The mass of an atom is primarily due to the protons and neutrons in the nucleus. The mass itself does not influence the number or behavior of valence electrons. Hence, this option does not affect the valence shell.

- **Option 4: Number of Core Electrons**
- Core electrons are the electrons in the inner shells. An increase in the number of core electrons can shield the valence electrons from the nuclear charge, thus affecting their energy levels and reactivity. Therefore, this option also affects the valence shell.

3. **Conclusion**:
- After evaluating all options, the only factor that does not affect the valence shell is **mass**.

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