Inactive Tutor answered 11/12/20
The larger the transition between energy levels, the more energy is absorbed or emitted.
However, as we know from the relationship between energy and wavelength, they are inversely proportional. Thus, the larger the transition, the more energy there is being produced, and thus the smaller the wavelength is.
Thus, the arrow with the longest transition (or spectrum line) will produce the lowest wavelength. The answer here will be D.

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thank you11/12/20