Calculate the number of electrons for each ion by adjusting for their charge:
- For Ba^{2+}, subtract 2 electrons from barium's atomic number (56).
- For I^{-}, add 1 electron to iodine's atomic number (53).
- For Te^{2-}, add 2 electrons to tellurium's atomic number (52).
- For Cs^{+}, subtract 1 electron from cesium's atomic number (55).