A piece of copper and a piece of germanium are cooled from room temperature 20 °C down to 80 K. The resistance of

copper decreases and that of germanium increases.

The correct answer is Option (4) → copper decreases and that of germanium increases.

Copper is a metal, and germanium is a semiconductor.

For metals:

→ As temperature decreases, the vibration of lattice ions reduces, causing resistance to decrease.

For semiconductors:

→ As temperature decreases, the number of thermally generated charge carriers decreases, causing resistance to increase.

∴ Correct answer: Copper decreases and that of germanium increases.