## Analytical Chemistry University of Florida final exam question, frequency difference

Question 20 from our final I just took (Analytical Chemistry UF).

"You may recall that the wavelength of the sodium D1 line in vacuum is 589.7558nm. In air it becomes 589.5924nm. What is the difference in frequency for these two wavelengths."

I said 0. All the other people did the math for the two wavelengths and subtracted them and got 1.409x10^11 Hz.

The test was multiple choice so they were both potential responses.

Am I right in assuming that the difference in their wavelengths was due to the change in speed of light in a vacuum vs air? And that the frequency is supposed to be constant for both? Or is this not the same thing?

Thx!
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