Answer is C , because current I = neav . n is no of free charge , which is increased with tha increase in temperature. and collision is also increase ,but free charge increase exponentially, so conductivity increase

Extrinsic semiconductors are materials that have been intentionally doped with impurities to alter their electrical properties. The conductivity of an extrinsic semiconductor is determined by the number of charge carriers (electrons or holes) available for conduction. The temperature affects the number of charge carriers and therefore the conductivity of the material.

Explanation:

1. Intrinsic Semiconductors:
Before discussing the behavior of extrinsic semiconductors with temperature, it is important to understand the behavior of intrinsic semiconductors. Intrinsic semiconductors are pure semiconducting materials without any intentional doping. At absolute zero temperature (0 Kelvin), the intrinsic semiconductor is in its purest form and there are no thermally generated charge carriers (electrons or holes). As the temperature increases, some electrons from the valence band gain enough energy to move to the conduction band, creating electron-hole pairs. This process is known as intrinsic carrier generation. As the temperature increases further, more electron-hole pairs are generated, leading to an increase in conductivity.

2. Extrinsic Semiconductors:
Extrinsic semiconductors are impurity-doped semiconductors. Two types of extrinsic semiconductors can be distinguished based on the nature of impurities:
- N-type Semiconductors: Doped with impurities that provide additional electrons as majority charge carriers.
- P-type Semiconductors: Doped with impurities that provide additional holes as majority charge carriers.

3. Conductivity in Extrinsic Semiconductors:
The conductivity of an extrinsic semiconductor is determined by the concentration of majority charge carriers. The concentration of charge carriers can be affected by temperature. In the case of extrinsic semiconductors, the behavior of conductivity with temperature is as follows:

- Option 'B': It decreases as temperature increases:
In an extrinsic semiconductor, the impurity atoms act as donor or acceptor atoms, providing additional charge carriers. As the temperature increases, the thermal energy also increases, enabling more electrons to gain enough energy to move to the conduction band. This means that the number of charge carriers increases with temperature. However, as the temperature increases, the thermal energy can also break some of the chemical bonds between the impurity atoms and the host atoms, reducing the concentration of impurity atoms and therefore the concentration of charge carriers. This reduction in the concentration of charge carriers leads to a decrease in conductivity as temperature increases.

Therefore, the correct answer is option 'B': It decreases as temperature increases.