Question

A ray of light at 90°on glass-air interface,then the light ray will...

Answer 1

When the ray of light is incident on the interface at 90 degrees, the angle of incidence, i = 0 degrees.
We know that, sin i = n * sin r {From Snells Law }

=> sin i = n*sin r = 0
=> sin r = 0
=> Angle of refraction , r = 0

Hence the ray passes through the glass air interface without any deviation.

Hope this helps :)