**Transparent Medium:**

A transparent medium is a medium that allows light to pass through it without significant scattering. It is the only correct option among the given choices because it meets the criteria for easy propagation of light.

**Explanation:**

When light passes through a transparent medium, it is able to propagate easily due to the material's optical properties. Let's discuss the characteristics of a transparent medium in detail:

1. **Clarity**: A transparent medium is clear, meaning it doesn't have any visible impurities or particles that would block or scatter light. This enables light to pass through without obstruction.

2. **Index of Refraction**: Transparent materials have a refractive index close to that of air or vacuum. The refractive index determines how much light bends when it enters the medium. A low refractive index allows light to pass through without significant deviation, resulting in easy propagation.

3. **Absorption**: Transparent materials have low absorption coefficients for visible light. This means that the material does not absorb or dissipate a significant amount of light energy as it passes through. Instead, it allows the light to travel through it, preserving its intensity and color.

4. **Atomic Structure**: In a transparent medium, the atoms or molecules are arranged in a regular and uniform manner. This regularity allows light to pass through without being scattered or absorbed by the individual particles.

Examples of transparent mediums include air, water, certain types of glass, and some plastics. These materials have the necessary properties to allow light to easily propagate through them, making them transparent.

**Importance of Transparent Mediums:**

Transparent mediums play a crucial role in our daily lives. They enable us to see clearly through windows, eyeglasses, and lenses. They also allow light to reach plants for photosynthesis and enable us to use optical devices such as microscopes, telescopes, and cameras.

In conclusion, a transparent medium is the correct answer as it meets the criteria for easy propagation of light. Its clarity, low absorption, and regular atomic structure allow light to pass through it without significant scattering or obstruction.