The elements 57 through 71 (Lanthanumand theLanthanoids) all form Ln 3ions in aqueous solution. These all have an electron configuration is [Xe]4fn where n increases from zero to fourteen over the series from Lanthanum to LutetiumSelect the two ions that have 4 unpaired spins.Eu3 Pr3 Er3 Pm3 Ho3 La3 Dy3 Tb3 Sm3 Tm3 Lu3 Gd3 Ce3 Yb3 Nd3
