The angle of refraction will be zero as the angle of incidence is zero in this case.... This is a rule,that whenever a ray striks perpendicularly or normally to a surface no reflection will take place......and hence and ray will pass through without deviating from its path....

Refraction of Light at 90° Angle of Incidence
When a ray of light enters from air to water at an angle of 90° (perpendicular to the interface), it will not refract. This is because when light travels from one medium to another at a 90° angle of incidence, there is no change in the speed of light, and hence no change in the direction of light.

Explanation
- When light travels from one medium to another, it changes its speed and direction due to the change in the refractive index of the two mediums.
- Refraction occurs when light enters a medium at an angle other than 90°, causing it to bend towards or away from the normal line depending on the refractive indices of the two mediums.
- At a 90° angle of incidence, the light ray is already perpendicular to the interface between air and water. This means that there is no change in the speed of light as it enters the water, resulting in no refraction.

Conclusion
In conclusion, when a ray of light enters from air to water at a 90° angle of incidence, it will not refract. This is because refraction occurs when there is a change in the speed of light, which is not the case at a 90° angle. Understanding the principles of refraction helps in predicting the behavior of light as it travels through different mediums at various angles of incidence.