The correct answer is A. Pure silicon.
The resistance of a material is a measure of how difficult it is for an electric current to flow through it. The resistance of most materials increases with increasing temperature. However, the resistance of pure silicon decreases with increasing temperature. This is because the electrons in silicon become more mobile as the temperature increases, which makes it easier for them to flow through the material.
Copper, nichrome, and platinum are all materials whose resistance increases with increasing temperature. This is because the electrons in these materials become less mobile as the temperature increases, which makes it more difficult for them to flow through the material.
Pure silicon is a semiconductor, which means that it has electrical properties that are intermediate between those of a conductor and an insulator. Semiconductors are used in a wide variety of electronic devices, including transistors, solar cells, and light-emitting diodes.