Atoms — Physics STD 12 Science — Question

4. nuclear magnetic spin

Explanation:
In atomic physics, hyperfine structure is the different effects leading to small shifts and splitting in the energy levels of atoms, molecules and ions.  The name is a reference to the fine structure which results from the interaction between the magnetic moments associated with electron spin and the electrons' orbital angular momentum. Hyperfine structure, with energy shifts is typically orders of magnitude smaller than the fine structure, results from the interactions of the nucleus (or nuclei, in molecules) with internally generated electric and magnetic fields.