Question

Which among the following elements has completely filled 4d-orbital?

• A. Ag
• B. Cd
• C. Sc
• D. Zr

Hint:

The elements at the very end of the d-block groups (Group 12: Zn, Cd, Hg) always have completely filled $\text{d}^{10}$ configurations along with fully filled $\text{s}^2$ shells!

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
We are given four transition metals and need to identify which element has a completely filled 4d subshell ($\text{4d}^{10}$) in its elemental ground state.

Step 2: Detailed Explanation:
Let's analyze the ground-state electronic configurations of the given elements using the Aufbau principle and exceptional stability rules:

• Scandium (Sc, Z = 21): Belongs to the 3d transition series. Its configuration is $[\text{Ar}] 3\text{d}^1 4\text{s}^2$. It does not possess electrons in the 4d orbital.

• Zirconium (Zr, Z = 40): Belongs to the 4d transition series. Its configuration is $[\text{Kr}] 4\text{d}^2 5\text{s}^2$. The 4d subshell is only partially filled.

• Silver (Ag, Z = 47): Exhibits an anomalous configuration due to the extra thermodynamic stability of a fully filled d-subshell. Its configuration is $[\text{Kr}] 4\text{d}^{10} 5\text{s}^1$. While its 4d shell is technically filled, it is the penultimate element of the series.

• Cadmium (Cd, Z = 48): Represents the final element of the 4d transition series. Its outer electronic configuration is $[\text{Kr}] 4\text{d}^{10} 5\text{s}^2$. Here, both the 4d orbital and the 5s orbital are completely filled.
Among the standard choices for completely filled d-orbitals finalizing a transition row, Cadmium represents a stable, closed d-shell system.

Step 3: Final Answer:
The element with a completely filled 4d orbital and a completed 5s valence shell is Cadmium, matching option (B).