Empirical formula is the simplest formula showing the simplest ratio of atoms in a compound. Calculated as shown;
we start by calculating the number of moles of each atom;
moles of nickel = 9.11 g ÷ 58.7 g = 0.155 moles
moles of fluorine = 5.89 g ÷ 19 g = 0.31 moles
Then we get the ratio of the moles of nickel to that of flourine
That is 0.155 : 0.31 (dividing by the smallest)
0.155/0.155 : 0.31/0.155
we get 1:2 ( the simplest ratio)
Therefore the empirical formula is nif2