Which of the following is a semiconductor?

The correct answer is (d), Germanium.

A semiconductor is a material that has electrical conductivity between that of a conductor and an insulator. Semiconductors are used to make a wide variety of electronic devices, including transistors, diodes, and integrated circuits.

Plastic is an insulator. It does not conduct electricity.

Aluminium is a conductor. It conducts electricity very well.

Wood is an insulator. It does not conduct electricity.

Germanium is a semiconductor. It has electrical conductivity between that of a conductor and an insulator.