What is the frequency of a light wave with a wavelength of 620nm

The color is orange.  

To find the frequency, we divide the speed of light (c) which is  

2.998 * 10**8 meters per second by the wavelength, here given as  

6.2 * 10**-7 meter. When we do the division we obtain  

4.835 * 10**14 cycles per second, or Hertz, as the frequency.  

Hope this answers your question.