The solubility order for alkali metal fluoride in water is :

$\mathrm{LiF}<\mathrm{NaF}<\mathrm{KF}<\mathrm{RbF}$

$\mathrm{LiF}>\mathrm{NaF}>\mathrm{KF}>\mathrm{RbF}$

$\mathrm{RbF}<\mathrm{KF}<\mathrm{NaF}<\mathrm{LiF}$

$\mathrm{LiF}<\mathrm{RbF}<\mathrm{KF}<\mathrm{NaF}$