16.   CaF2 is least/most soluble in which of the following solutions?
a)   0.10 M Ca(NO3)2   b) 0.20 M Ca(NO3)2     c) 0.10 M NaF       d) 0.10 M water
==>
Least Soluble a) --It will dissolve worst in Ca(NO3)2 solution due to the common ion effect.
Most Soluble   c)--Calcium fluoride is slightly basic and will dissolve best in acid solutions

please advise if this is correct

Sp(CaF2) = 4* 10^-13 (mol/l)^3

Sp = cCa2+ * (cF-)^2
If you solve then you will f?nf NaF  is the best and water the worst.

Quote from: prasamb@yahoo.com on March 29, 2023, 10:23:44 AM
16.   CaF2 is least/most soluble in which of the following solutions?
a)   0.10 M Ca(NO3)2   b) 0.20 M Ca(NO3)2     c) 0.10 M NaF       d) 0.10 M water
==>
Least Soluble a) --It will dissolve worst in Ca(NO3)2 solution due to the common ion effect.
Most Soluble   c)--Calcium fluoride is slightly basic and will dissolve best in acid solutions

please advise if this is correct

CaF₂(s)  <---> Ca²⁺ (aq)  + 2F^- (aq)

Due to common ions , solubility equilibrium shifts in left which means less solubility.0.2 M Ca(NO3)2 is the worst because it is giving very large concentration of Ca²⁺ ions.
Water is the best because it decreases the concentration of ions in the solution and equilibrium shifts to right and hence solubility increases.