b. Blue.
This is second of two questions with some calculations involved:
The wavelength of this light is:
Using:
v=fl
We can divide both sides by f to get:
l=v/f
Or:
l=(3 x 108 m/s)
/(7.5 x 1014 1/sec) = 400 x 10-9 m, or 400
nm. That's near the blue end of the spectrum (See tutorial 1, chapter 4
of FEU text.)