Which transition has energy < 210 nm?
Photon energy inversely proportional to wavelength, so shorter wavelength means higher energy. In carbonyls, amides and heteroaromatics, forbidden n→π* transition promotes lone pair electron to antibonding π* orbital, requiring relatively low energy and appearing at longer wavelengths around 270-300 nm, beyond 210 nm threshold. Therefore energy associated with 210 nm photon exceeds that needed for n→π*, placing n→π* on low-energy side of spectrum, distinct from high-energy σ→σ* below 150 nm. Understanding this ordering helps assign absorption bands, predict solvent effects and rationalize photochemical reactivity of biological carbonyl compounds.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.