Step 1: Define a semiconductor.
A semiconductor is a material that has electrical conductivity between that of a conductor (like metals) and an insulator (like diamond). Their conductivity can be increased by adding impurities (doping) or by increasing temperature.
Step 2: Analyze each option.
\begin{itemize} \item (1) Fe (Iron): Iron is a metal. Metals are good conductors of electricity due to the presence of free electrons in their metallic bonds. \item (2) Ge (Germanium): Germanium is a metalloid (or semi-metal) and is a well-known semiconductor. It has properties intermediate between metals and non-metals in terms of electrical conductivity. Its conductivity increases with temperature and can be significantly enhanced by doping. \item (3) Diamond (Carbon): Diamond is an allotrope of carbon. In diamond, each carbon atom is covalently bonded to four other carbon atoms in a strong tetrahedral network. There are no free electrons, making diamond a good electrical insulator. \item (4) Cu (Copper): Copper is a transition metal and is an excellent conductor of electricity due to the presence of mobile electrons in its metallic lattice.
\end{itemize}
Step 3: Identify the semiconductor.
Among the given options, Germanium (Ge) is a semiconductor. Final Answer: