What is the nuclear spin quantum number (I) for ¹H?
Protium nucleus contains one proton with odd mass number, producing intrinsic spin quantum number one-half. Quantum spin generates a magnetic moment with two Zeeman orientations, +1/2 and -1/2, in external magnetic field, permitting resonant radiofrequency absorption central to NMR. Nuclei with even protons and neutrons possess zero spin, while odd-odd combinations yield integer spins. Half-integer spin confers high gyromagnetic ratio and abundant sensitivity, making hydrogen indispensable for protein, metabolite, water, and lipid detection in biological NMR experiments and medical MRI imaging.
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.