Step 1: Understanding the Concept:
Elements where the last differentiating electron enters the $(\text{n}-1)\text{d}$ subshell are called d-block elements (transition metals).
Step 2: Key Formula or Approach:
Check blocks: d-block vs f-block.
Step 3: Detailed Explanation:
- (A) Dy (Dysprosium): Lanthanide, f-block. Last electron enters $(\text{n}-2)\text{f}$ i.e., $4\text{f}$.
- (B) Ag (Silver): Transition metal, d-block. It's in the second transition series ($4\text{d}$ series). Configuration: $[\text{Kr}] 4\text{d}^{10} 5\text{s}^1$. The last electron conceptually fills the $4\text{d}$ subshell (where $\text{n}=5$).
- (C) Pu (Plutonium): Actinide, f-block.
- (D) Pa (Protactinium): Actinide, f-block.
Step 4: Final Answer:
For Ag, the last electron is placed in the $(\text{n}-1)\text{d}$ orbital.