Zn and Cd metals do not show varible valency because:

Options

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

Answer

To understand why Zinc (Zn) and Cadmium (Cd) do not show variable valency, we can analyze their electronic configurations and the stability of their d-orbitals.

### Step-by-Step Solution:

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

2. **Analyze the d-Orbitals**:
- In both Zn and Cd, the d-orbitals are completely filled:
- For Zn: The 3d subshell has 10 electrons (3d^10).
- For Cd: The 4d subshell also has 10 electrons (4d^10).
- A completely filled d-orbital is highly stable and does not easily lose electrons.

3. **Determine the Valency**:
- The valency of an element is determined by the number of electrons it can lose or gain during chemical reactions.
- In the case of Zn and Cd, they can lose the two electrons from their outermost s-orbital (4s for Zn and 5s for Cd) to form compounds.
- Therefore, both Zn and Cd typically exhibit a valency of +2.

4. **Conclude the Reason for Lack of Variable Valency**:
- Since both metals have completely filled d-orbitals, they do not exhibit variable valency. Instead, they consistently show a +2 oxidation state.
- Hence, the correct reason for the lack of variable valency in Zn and Cd is that their d-subshells are completely filled.

### Final Answer:
Zinc and Cadmium do not show variable valency because their d-subshells are completely filled.