Question

What is the longest-wavelength line in nanometers in the infrared series for hydrogen where m=3?

Answer 1

If n=3
then it is called PASCHEN RAYS
n₁=3 and n₂=4,5,6 and so on
Longest wavelength at n₂=INFINITY is 820.4nm
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Answer 2

We know that energy is inversely proportional to wavelength .so longest wavelength line means least energy line.
In the given case inner shell is 3rd so smallest energy difference will occur when outer shell will be 4th...and Hence longest wavelength line is obtained when outer shell is 4th and inner shell is 3rd..