Explanation:

Transpiration is the process by which water is lost from the leaves of a plant in the form of water vapor. It is an important process for plants as it helps in the absorption and transport of water and nutrients from the roots to the rest of the plant.

The rate of transpiration is affected by various environmental factors. Let's discuss each option and its impact on transpiration:

a) High wind velocity:
- High wind velocity increases the rate of transpiration.
- When there is a high wind velocity, the boundary layer of still air around the leaf is reduced, which increases the rate of water vapor diffusion from the leaf surface.
- As a result, transpiration increases.

b) Good soil moisture:
- Good soil moisture provides an adequate water supply to the plant.
- When the soil moisture is sufficient, the plant does not need to transpire as much to meet its water requirements.
- Therefore, transpiration is lower when the soil moisture is good.

c) Dry environment:
- In a dry environment, the rate of transpiration is high.
- When the surrounding air is dry, the water potential gradient between the leaf and the atmosphere increases.
- This gradient drives the movement of water vapor from the leaf to the atmosphere through the process of transpiration.

d) High atmospheric humidity:
- High atmospheric humidity reduces the rate of transpiration.
- When the surrounding air is already saturated with water vapor, there is a reduced water potential gradient between the leaf and the atmosphere.
- As a result, the movement of water vapor from the leaf to the atmosphere is slower, leading to lower transpiration rates.

Conclusion:

Out of the given options, high atmospheric humidity (option D) is the condition that leads to the least transpiration. In a high-humidity environment, the reduced water potential gradient restricts the movement of water vapor from the leaf surface to the atmosphere, resulting in lower transpiration rates.