*Question E6F06:
Which of these materials is most commonly used to create photoconductive devices?*  

*Correct Answer is  C: Crystalline semiconductor*  

### AI Response: (may contain errors)  

Photoconductive devices are components that change their electrical resistance when exposed to light. The most common material used for these devices is a crystalline semiconductor. Here's why:

1. **Correct Answer: Crystalline Semiconductor**
   - **Explanation**: Crystalline semiconductors, such as silicon or cadmium sulfide, have properties that allow their electrical conductivity to change significantly when exposed to light. This makes them ideal for use in photoconductive devices like photodetectors and light-dependent resistors (LDRs).

2. **Why Other Choices Are Incorrect**:
   - **Polyphenol Acetate**: This is a type of plastic, not typically used for photoconductive applications. It lacks the necessary electronic properties to change conductivity with light exposure.
   - **Argon**: Argon is an inert gas and does not have the solid-state properties required for photoconductivity. It is used in lighting and as a shielding gas in welding, but not in photoconductive devices.
   - **All these choices are correct**: This option is incorrect because only crystalline semiconductors are suitable for creating photoconductive devices.

In summary, crystalline semiconductors are the most suitable materials for photoconductive devices due to their ability to change electrical properties in response to light.