the one with 81 as the smaller number.... if there isen't one, then you've got your calculations wrong...
No . all the atoms have same no of protones.....
Thallium.
81/36 kr
This chemical element is thallium.
Thallium, Tl
6
Element 81 is thallium.
Barium
Barium.
Thallium (Tl)
This chemical element is krypton.
Thallium. Atomic number (Z) = 81