Which of the following material is not a semiconductor.

Solution

Chemistry ma’am · 3 steps

Graphite has a free electron on every carbon, so it conducts like a metal, not like a semiconductor.

1. What a semiconductor is. A semiconductor conducts only a little at room temperature, and it conducts more as it gets hotter. Its conductivity lies between that of insulators and metals.
2. Look at graphite. In graphite each carbon is sp² hybridised and uses only three electrons for bonds inside its layer. The fourth electron is delocalised over the whole layer, so it moves freely and carries current like the electrons in a metal.

   Material	Electrical behaviour	Semiconductor?
   Copper oxide	small conductivity, rises with temperature	yes
   Graphite	free delocalised electrons, conducts like a metal	no, it is a conductor
   Silicon	small conductivity, rises with temperature	yes
   Germanium	small conductivity, rises with temperature	yes

3. So. Silicon, germanium and copper oxide are all semiconductors. Graphite, option (b), is a good conductor and is the odd one out.

The idea to keep. Carbon is in the same group as Si and Ge, but graphite is not a semiconductor. Its delocalised electrons make it a conductor, which is why it is used for electrodes.

Answer from the NTA final answer key. Solution by PrepWiser.