Answer:
Option B. 176g/mol 
Step-by-step explanation:
We'll begin by writing the chemical formula for hexasodium difluoride. This is given below:
Hexasodium means 6 sodium atom 
Difluoride means 2 fluorine atom.
Therefore, the formula for hexasodium difluoride is Na6F2.
The relative formula mass of a compound is obtained by simply adding the atomic masses of the elements present in the compound. 
Thus, the relative formula mass of hexasodium difluoride, Na6F2 can be obtained as follow:
Molar mass of Na = 23g/mol 
Molar mass of F = 19g/mol 
Relative formula mass Na6F2 = (23x6) + (19x2)
= 138 + 38
= 176g/mol 
Therefore, the relative formula mass of hexasodium difluoride, Na6F2 is 176g/mol