The addition of which solution will shift the equilibrium of the given equation?
caf2 (s) mc031-1.jpg ca2+ (aq) + 2f– (aq)

1)0.1 m ba(no3)2
2)0.1 m mgcl2
3)0.1 m kc2h3o2
4)0.1 m naf

0.1 M NaF

Explanation:  Solubility of calcium fluoride would decrease if we add a compound that has a common ion(either calcium or fluoride). We call it common ion effect.

If we look at the first three choices then none of these have any common ion but the last one that is NaF has one common ion(fluoride ion).

So, if NaF is added to calcium fluoride then the given equilibrium reaction will shift to the left means the solubility of calcium fluoride decreases since the fluoride ion comes into the solution by more soluble sodium fluoride.