**Aquaplaning** occurs when the vehicle's tires cannot displace all the water from the road, causing the vehicle to lose contact with the ground and skid. This results in a **loss of grip**, especially in conditions of heavy rain.

- The loss of grip is more likely if driving at high speed or if the tires are worn or very wide. Therefore, it is important to reduce speed in areas with water to avoid aquaplaning.
- Additionally, when it rains, tires generally have less grip on the road, which also contributes to the loss of grip and means the vehicle needs more space to brake.

Therefore, aquaplaning is a phenomenon that clearly causes a **loss of grip in case of rain**, confirming that the correct answer is the first option.