1. Find the atomic masses of each element:

* Ni (Nickel): 58.6934 g/mol

* F (Fluorine): 18.9984 g/mol

2. Multiply the atomic mass of each element by its subscript in the formula:

* Ni: 1 x 58.6934 g/mol = 58.6934 g/mol

* F: 2 x 18.9984 g/mol = 37.9968 g/mol

3. Add the results together:

58.6934 g/mol + 37.9968 g/mol = 96.6902 g/mol

Therefore, the formula mass of NiF₂ is 96.6902 g/mol.