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 Zn (Zinc) and Cd (Cadmium) metals do not show variable valency, we can follow these steps:

### Step 1: Understand the Electronic Configuration
- **Zinc (Zn)** has an atomic number of 30. Its electronic configuration is:
- \( \text{Zn: } [\text{Ar}] 4s^2 3d^{10} \)
- **Cadmium (Cd)** has an atomic number of 48. Its electronic configuration is:
- \( \text{Cd: } [\text{Kr}] 5s^2 4d^{10} \)

### Step 2: Analyze the d-Orbital Filling
- Both Zn and Cd have fully filled d-orbitals:
- For Zn, the 3d subshell is completely filled with 10 electrons.
- For Cd, the 4d subshell is also completely filled with 10 electrons.

### Step 3: Understand the Concept of Variable Valency
- Variable valency occurs when elements can lose different numbers of electrons from their outer shell and d-orbitals, leading to different oxidation states.
- In elements where the d-orbitals are not fully filled, they can exhibit variable valency by losing different numbers of electrons.

### Step 4: Conclusion on Variable Valency for Zn and Cd
- Since both Zn and Cd have fully filled d-orbitals, they do not have the ability to lose electrons from the d-orbitals to form different oxidation states.
- Therefore, they predominantly exhibit a fixed oxidation state:
- Zn typically shows a +2 oxidation state.
- Cd typically shows a +2 oxidation state as well.

### Final Answer
Zn and Cd do not show variable valency because their d-subshells are completely filled (3d^{10} for Zn and 4d^{10} for Cd), which prevents them from losing different numbers of electrons to form various oxidation states.

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