Which of the following elements is a semiconductor?

1. A

   Aluminium

   Aluminium is a metal and a good electrical conductor, used in power lines. It is not a semiconductor. This option is not the key.

2. B

   Silicon

   Silicon is a group-14 metalloid and the principal elemental semiconductor of the electronics industry. Its conductivity lies between metals and insulators and is tunable by doping. This option is the official key.

3. C

   Silver

   Silver is the best metallic electrical conductor among common metals, not a semiconductor. This option is therefore wrong.

4. D

   Lead

   Lead is a metal. It is not used as a semiconductor wafer material. This option is not the key.

Summary. Official key is (b) Silicon. Semiconductors have resistivity between conductors and insulators; silicon and germanium are the classic elemental examples. Aluminium, silver and lead are metals and conduct freely. Only silicon in this list is a semiconductor.