Question

What is the approximate range of wavelengths for visible light?

Answer 1

We can answer the question by looking at the spectrum of the visible light, for example in this figure:
https://en.wikipedia.org/wiki/Light#/media/File:EM_spectrum.svg

We see from the figure that the lowest part of the spectrum (violet) corresponds approximately to a wavelength of 380 nm, while the highest part of the spectrum (red light) corresponds approximately to a wavelength of 750 nm.