posted by Grace .
What is the Wavelength( in nm) of the least energetic spectral line in the infrared series of the H atom?
I don't understand how to find the least energetic spectral line?
I don't know if the question wants the least energetic line (IN THE INFRARED) or the least energetic line (where ever that may be) in the spectrum in which in infrared line appears. Perhaps this link will help you.
The 1094 nm line is an infrared line in my book.