Molarity is simply the number of moles dissolved per liter of solution.
Converting the mass of LiF to moles:
52 g / 26 g/mol = 2 mol LiF
Next, simply divide the number of mole by the volume
2 mol / 1.5 L = 1.3333 mole/L
So, the molarity of the given solution is 1.3333 M