Identify the element from following such that the last electron is placed in ( $\mathrm{n}-1$ ) d orbital.

The element where the last electron occupies the $(\mathrm{n}-1)$ d orbital can be identified by examining electronic configurations of the given options.

The general configuration for d-block elements is $(\mathrm{n}-1) \mathrm{d}^{1-10} \mathrm{ns}^{1-2}$, where $n$ denotes the principal quantum number of the outermost shell.

Dysprosium (Dy, $Z=66$) has configuration $[\mathrm{Xe}] 4\mathrm{f}^{10} 6\mathrm{s}^{2}$ and is a lanthanide where the last electron enters the $4\mathrm{f}$ orbital.

Silver (Ag, $Z=47$) has configuration $[\mathrm{Kr}] 4\mathrm{d}^{10} 5\mathrm{s}^{1}$ with outermost shell $n=5$. The $4\mathrm{d}$ orbital corresponds to $(n-1)\mathrm{d}$, confirming d-block classification.

Plutonium (Pu, $Z=94$) has configuration $[\mathrm{Rn}] 5\mathrm{f}^{6} 7\mathrm{s}^{2}$ and is an actinide with last electron in the $5\mathrm{f}$ orbital.

Protactinium (Pa, $Z=91$) has configuration $[\mathrm{Rn}] 5\mathrm{f}^{2} 6\mathrm{d}^{1} 7\mathrm{s}^{2}$ but its characteristic differentiating electron is in the $5\mathrm{f}$ orbital, classifying it as f-block.

Silver is the element where the last electron occupies the $(\mathrm{n}-1)$ d orbital.