The meter has been defined as 1,650,763.73 wavelengths of the orange-red line of the emission spectrum of ^86Kr. Calculate the frequency of this radiation. In what proportion of the electromagnetic spectrum does the radiation fall?

What is the wavelength of the Kr line? That is 1 m = 1,650,763.73 x wavelength. Solve for wavelength. Then

c = freq*wavelength
wavelength is from above.
c = 3E8 m/s
Solve for freq.
Obviously if it is an orange-red line it must be in the visible part of the spectrum.
By the way, I think you meant, "In what PORTION of .....".

I got 5.506x10^-3 when I divide the wavelength by the speed of light but I don't think that's right because Kr is an isotope. Could you please explain how this works too?

Not what I get. What is the wavelength you have. Post your work and I'll find the error.

Oh is it 1.816x10^2? I divide the speed of light by the wavelength: 2.998x10^8 / 1,650,763.73
I did the reverse the first time. Is this correct now?

No. 1,650,763.73 is not the wavelength. Look at my first response again.
1 m = 1,650,763.73 x wavelength and you calculate the wavelength from that. Frequency is in the order of 10^14 Hz unless I punched te wrong buttons.

ok so for wavelength I get 6.058x10^-7
then I divide: 2.998x10^8 / 6.058x10^-7 and get 4.949x10^14 Hz
Is this correct?

Looks ok to me.

Thank you for your help

I didn't think to post the earlier but since you have so many significant figures in the wavelength calculation, you could use that many places in the speed of light. I don't know that many places but I know it's available on the web.

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how did you get 6.058x10^-7?