The stability of dihalides of $Si,Ge,Sn$ and $Pb$ increases steadily in the sequence :
$Pb{X_2} < < Sn{X_2} < < Ge{X_2} < < Si{X_2}$
$Ge{X_2} < < Si{X_2} < < Sn{X_2} < < Pb{X_2}$
$Si{X_2} < < Ge{X_2} < < Pb{X_2} < < Sn{X_2}$
$Si{X_2} < < Ge{X_2} < < Sn{X_2} < < Pb{X_2}$
