Answer:
Step-by-step explanation:
This is not the exact definition of a formula unit, but I think I know what is meant. You want the number of mols that 33.8 grams represents.
1 mol of SrF2
1 unit of Sr = 87.62
2 units of F = 19.00 * 2 = 38.00
1 mol of SrF2 = 125.62
mols SrF2 = given mass / molar mass
given mass = 33.8
Molar mass = 125.62
mols = 33.8/125.62 = 0.269