Answer :
As a monochromatic light ray passes from air into water, two characteristics of the ray that will not change are "(1) wavelength and period" which are inherent to the wave.
The correct answer is
(2) frequency and period
In fact, when a light wave moves from one medium to another, its speed and its wavelength change. On the contrary, the frequency of the wave remains the same. Since the period is the reciprocal of the frequency:
[tex] T=\frac{1}{f} [/tex]
this means that the period of the wave does not change neither. So, the correct answer is
(2) frequency and period
