Correct Answer:
A. Frequency
When light undergoes refraction, it passes from one medium to another, causing its speed and direction to change. This change in speed also affects its wavelength, as speed (v) is directly proportional to wavelength (λ) when frequency (f) is constant (v = fλ). However, the frequency of light is determined by its source and remains constant regardless of the medium it travels through. Therefore, frequency does not change during refraction. Amplitude, which relates to the intensity of light, can change due to energy loss or reflection at the interface, but it is not the fundamental constant like frequency.