Which of the following shows hypochromic effect?
Intensity changes in UV spectra describe chromicity effects independent of wavelength shift. Hyperchromic effect indicates increase in molar absorptivity ε and measured absorbance, famously observed during DNA thermal denaturation when double helix unwinds, base stacking disrupted and π interactions lessen, raising ε. Hypochromic effect indicates decrease in absorbance when chromophores become ordered, stacked or shielded, as in double-stranded DNA formation or protein folding bringing aromatic residues into defined environment causing electronic coupling and shielding. Hypochromicity quantifies hybridization, secondary structure formation and is central for melting temperature determination in molecular biology investigations.
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.