Zn and Cd metals do not show varible valency because:

Options

A. They have only two electrons in the outermost subshells
B. Their d-subshells are completely filled
C. Their d-subshells are partially filled
D. they are relatively soft metals

Answer

To answer the question of why zinc (Zn) and cadmium (Cd) do not show variable valency, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Electronic Configurations**:
- The electronic configuration of Zinc (Zn) is:
\[ \text{Zn: } [\text{Ar}] 3d^{10} 4s^2 \]
- The electronic configuration of Cadmium (Cd) is:
\[ \text{Cd: } [\text{Kr}] 4d^{10} 5s^2 \]

2. **Determine the Common Oxidation State**:
- Both Zn and Cd have a tendency to lose their outermost s-electrons (4s for Zn and 5s for Cd).
- When they lose these two s-electrons, they achieve a common oxidation state of +2:
\[ \text{Zn}^{+2}: [\text{Ar}] 3d^{10} \quad \text{and} \quad \text{Cd}^{+2}: [\text{Kr}] 4d^{10} \]

3. **Analyze the Stability of the d-Orbitals**:
- After losing the s-electrons, both metals have completely filled d-orbitals (10 electrons in the d-orbitals).
- A completely filled d-orbital configuration is particularly stable.

4. **Consider Ionization Energy**:
- The stability of the filled d-orbitals means that it requires a significant amount of energy (high ionization energy) to remove any additional electrons from these orbitals.
- This high ionization energy makes it difficult for Zn and Cd to exhibit variable valency, as they cannot easily lose electrons beyond the +2 oxidation state.

5. **Conclusion**:
- Therefore, the reason Zn and Cd do not show variable valency is that they have completely filled d-orbitals, which leads to high ionization energies, making it difficult to remove additional electrons.

### Final Answer:
Zn and Cd do not show variable valency because they have completely filled d-orbitals, resulting in high ionization energy that prevents the removal of additional electrons beyond the +2 oxidation state.

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