Visible light is a portion of the electromagnetic spectrum, that includes wavelengths approximately from 380 nm to 750 nm.
It is the only part of the electromagnetic spectrum that the human eye can see. Depending on the wavelength of the light in this region, we perceive the light as a different color.
Therefore, each color is associated to a different range of wavelength, as follows:
The mass number is
238
, so the nucleus has <u>238 particles</u> in total, including <u>146 neutrons</u>. So to calculate the number of neutrons we have to subtract: 238 − 146 = 92