Overview:
Total internal reflection is a phenomenon that occurs when light travels from a denser medium to a rarer medium and is incident at an angle greater than the critical angle. In this process, the light undergoes reflection at the boundary between the two media, without any loss of intensity.

Denser to Rarer Medium:
In total internal reflection, the light travels from a denser medium to a rarer medium. This means that the medium through which the light is initially propagating has a higher refractive index compared to the medium it is entering.

No Loss of Intensity:
During total internal reflection, the light experiences reflection at the boundary between the two media. This reflection occurs without any loss of intensity. This means that the amount of light energy remains constant during this process.

Explanation:
1. When light travels from a denser medium to a rarer medium, it bends away from the normal at the boundary between the two media. This bending is a result of the change in speed and change in direction of light due to the difference in refractive indices.
2. As the angle of incidence increases, the angle of refraction also increases. At a certain angle of incidence, known as the critical angle, the angle of refraction becomes 90 degrees.
3. When the angle of incidence is greater than the critical angle, the light undergoes total internal reflection. This means that instead of refracting into the rarer medium, the light is completely reflected back into the denser medium.
4. Total internal reflection occurs due to the principle of conservation of energy. Since the refractive index of the rarer medium is lower, the speed of light in the rarer medium is higher. For total internal reflection to occur, the angle of incidence must be greater than the critical angle, ensuring that the light cannot escape into the rarer medium.
5. The phenomenon of total internal reflection is widely used in optical devices such as fiber optics and prisms. It allows for efficient transmission and manipulation of light without significant loss of intensity.
6. It is important to note that total internal reflection only occurs when light travels from a denser medium to a rarer medium. If the light travels from a rarer medium to a denser medium, it will undergo refraction instead of reflection.

Therefore, the correct answer is option 'B' - Total internal reflection occurs when light travels from a denser to a rarer medium, and it occurs with no loss of intensity.