As monochromatic light passes from air to glass and back to air changes are observed in its

A. Wavelength and frequency
B. Wavelength, frequency, and speed
C. Frequency and speed
D. Wavelength and speed
E. None of these

The speed and wavelength of light changes as it passes from one medium to another, but the frequency stays constant. As it travels from air to glass both the speed and wavelength are reduced by a factor n=index of refraction of glass, and since speed = frequency * wavelength this means that the frequency stays the same. As the light emerges from the glass to air then all of its characteristics return to the same as they were before entering the glass. The actual question is a little ambiguous but basically when light travels from one medium to another then it is answer D. that occurs.