During, refraction ___ will not change.
frequency
Explanation for correct option:
In case of option A, frequency is the characteristic property of the source of light. It does not depend on the medium, so it will not change.
Explanation for incorrect options:
In case of option B, the wavelength of light depends on the medium and it changes accordingly.
In case of option C, the speed of light also depends on the medium and it becomes slower in a denser medium and vice-versa.
In case of option D, since wavelength and speed do change during refraction, so this option is incorrect.
Thus, during refraction frequency will not change.
So, option A is the correct answer.