Due to the small and highly electronegative nature of fluorine, the oxyacids of the this element are much less common and less stable than those of the other halogens. Bonding theory, however, does allow one to propose structures for these acids and use formal charges for the evaluation of these structures. For a molecule of fluorous acid, the atoms are arranged as HOFO. (Note: In this oxyacid, the placement of fluorine is an exception to the rule of putting the more electronegative atom in a terminal position.) What is the formal charge on each of the atoms?

HOFO = (0, 0, +1, -1)

Explanation:

The formal charge (FC) can be calculated using the following equation:

Where:

V: are the valence electrons

N: are the nonbonding electrons

B: are the bonding electrons

The arrange of the atoms in the oxyacid is:

H - O₁ - F - O₂

Hence, the formal charge (FC) on each of the atoms is:

H: FC = 1 - 0 - 1/2*(2) = 0            

O₁: FC = 6 - 4 - 1/2*(4) = 0        

F: FC = 7 - 4 - 1/2*(4) = +1

O₂: FC =  6 - 6 - 1/2*(2) = -1

We can see that the negative charge is in the oxygen instead of the most electronegative element, which is the F. This oxyacid is atypical.  

I hope it helps you!