How can we measure electronic excitation in some "nm"(nanometres)?

I have no idea to which concept this belongs:



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> The widest range over which electronic excitations in organic compounds occur, is
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> A) 200 nm – 780 nm
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> B) 220 nm– 500nm 
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> C) 250 nm– 700 nm
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> D) 290 nm – 1000nm
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> 




The question is asking what wavelengths of light can cause electronic excitation in organic compounds, i.e. what energy photons correspond to the energy difference between the ground and excited states. They're not the same in all compounds (which is why different compounds have different absorbance spectra), but there is a range of energies in which most of the electronic transitions in organic compounds occur.


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