When light waves pass from air to glass, the variables affected are the wavelength and velocity of the light waves. The correct answer is option 'D' - wavelength and velocity.

1. Wavelength:
When light waves pass from one medium to another, such as from air to glass, the wavelength of the light waves changes. The wavelength is the distance between two consecutive peaks or troughs of a wave. In air, the light waves have a certain wavelength, but when they enter the glass, the wavelength decreases. This change in wavelength is due to the change in the refractive index of the two mediums.

2. Refractive Index:
The refractive index is a measure of how much a medium can bend or refract light. Each medium has a specific refractive index, and when light waves pass from one medium to another, they experience a change in speed and direction. The refractive index of glass is higher than that of air, so when light waves enter glass, they slow down and change direction.

3. Velocity:
The velocity of light waves is affected by the change in refractive index between air and glass. In air, light waves travel at a certain speed, which is approximately 3 x 10^8 meters per second. However, when light waves enter glass, their velocity decreases. This decrease in velocity is due to the higher refractive index of glass compared to air.

4. Snell's Law:
The change in velocity and wavelength of light waves when passing from one medium to another is described by Snell's Law. According to Snell's Law, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the ratio of the velocities in the two mediums. This law explains how light waves bend or refract when passing through different mediums.

In conclusion, when light waves pass from air to glass, the variables affected are the wavelength and velocity of the light waves. The wavelength decreases and the velocity decreases when light waves enter the glass medium.