text: A<unk>  is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons. A<unk>  occupies a higher energy state than the corresponding non-excited nucleus, called the ground state. The<unk>  will eventually release the extra energy and decay into the ground state.
option_0: Nuclear isomer
option_1: Complex 
option_2: Heterocyclic compound
option_3: Mosaic 
option_4: Isomer
option_5: Cyclic compound
option_6: Diradical
option_7: Isotopomers