# $Ce^{3+} , \; La^{3+}, \; Pm^{3+}$ and $Yb^{3+}$ have ionic radii in the increasing order as :
( A ) $La^{3+} < Ce^{3+} < Pm^{3+} < Yb^{3+}$
( B ) $La^{3+} = Ce^{3+} < Pm^{3+} < Yb^{3+}$
( C ) $Yb^{3+} < Pm^{3+} < Ce^{3+} < La^{3+}$
( D ) $Yb^{3+} < Pm^{3+} < La^{3+} < Ce^{3+}$