Photosensitive semiconductors are the semiconductors that change their conductivity or electrical resistance when exposed to light. The conductivity of a photosensitive semiconductor is affected by the light falling on it, and the number of electrons present in the semiconductor. The correct answer to this question is option 'C', which states that the conductivity of a photosensitive semiconductor increases with light.

Explanation:

When light falls on a photosensitive semiconductor, the energy from the light is absorbed by the semiconductor. This absorbed energy promotes electrons from the valence band to the conduction band, creating electron-hole pairs.

Electron-hole pairs:
- The conduction band is the band of energy levels that electrons can occupy when they are excited or promoted by an external energy source, such as light.
- The valence band is the band of energy levels that electrons occupy when they are at rest or not excited.
- The energy gap between the valence band and the conduction band is called the bandgap.

When an electron is promoted to the conduction band, it leaves behind a hole in the valence band. The electron and the hole are free to move around the semiconductor, and they contribute to the semiconductor's electrical conductivity.

Effect of light on conductivity:
- When light falls on a photosensitive semiconductor, it promotes more electrons to the conduction band, creating more electron-hole pairs.
- This increase in the number of electron-hole pairs increases the conductivity of the semiconductor.
- Therefore, the conductivity of a photosensitive semiconductor increases with light.

Conclusion:
The conductivity of a photosensitive semiconductor is affected by the light falling on it and the number of electrons present in it. As light falls on a photosensitive semiconductor, it promotes more electrons to the conduction band, creating more electron-hole pairs, and increasing the semiconductor's conductivity. Therefore, the correct answer to this question is option 'C', which states that the conductivity of a photosensitive semiconductor increases with light.