The formal charge of an atom in a molecule is the charge that the atom would have if all of the bonds to it were broken and the electrons were divided equally between the atoms.

To calculate the formal charge of an atom, we first need to know the number of valence electrons that the atom has. Then, we need to know the number of electrons that the atom has bonded to other atoms. Finally, we need to know the number of lone pairs of electrons that the atom has.

The formal charge of an atom is calculated as follows:

Formal charge = (number of valence electrons) - (number of bonded electrons) - (number of lone pairs of electrons)

For GeF6 2-, the formal charges are as follows:

Ge: 4 valence electrons - 6 bonded electrons - 0 lone pairs of electrons = +2 formal charge

F: 7 valence electrons - 1 bonded electron - 3 lone pairs of electrons = -1 formal charge

The sum of the formal charges of all of the atoms in a molecule must be equal to the overall charge of the molecule. In this case, the overall charge of GeF6 2- is -2, so the sum of the formal charges of the Ge and F atoms must also be -2.