Hmm… I don’t think knowledge of the different wavelengths of different colours of light is in the primary school syllabus.
- Across the ROYGBIV spectrum, different colours of light have different wavelengths and energy levels
- Among the three lights used in the experiment, red light has the longest wavelength (and least energy), followed by green light, then blue light
- The water molecules preferentially absorb light with longer wavelengths so it is less visible
- Shorter wavelengths with more energy can better penetrate water depths so they more visible to our eyes
All of those points above require some knowledge not in the primary school syllabus, so if I were to answer this question as a primary 6 student, I would probably just say:
- Blue light can penetrate water better than green and red light, with red light being the least able to do so.