Question
The solubility order for alkali metal fluoride in water is :
A.
$$LiF < RbF < KF < NaF$$
B.
$$RbF < KF < NaF < LiF$$
C.
$$LiF > NaF > KF > RbF$$
D.
$$LiF > NaF < KF < RbF$$
Answer :
$$LiF > NaF < KF < RbF$$
Solution :
Higher the lattice enthalpy lower will be solubility i.e.,
$${\text{lattice enthalpy}} \propto \frac{1}{{{\text{Solubility}}}}$$
Since the lattice enthalpy of alkali metals follow the order
$$Li > Na > K > Rb$$
Hence the correct order of solubility is
$$LiF < NaF < KF < RbF$$