Protoactinium (Pa) is the element that does not have stable electronic configuration. Protoactinium (Pa)=[Rn]5f26d17s2( Atomic number =91) Nobelium (No)=[Rn]5f146d07s2( Atomic number =102) Lawrencium (Lr)=[Rn]5f146d17s2 (Atomic number =103 ) Amercium (Am)=[Rn]5f76d07s2 (Atomic number =95 )