What is the formal charge on the bromine atom in hbr?

Formal Charge is defined as the charge an atom in a molecule has, assuming that whatever the electronegativity, the electrons in all chemical bonds are shared equally between atoms.

It can be calculated as: number of valence electrons - number of bonds - number of electrons surrounding Br in the Lewis structure.

The number of valence electrons of Bromine is 7.

The number of bonds is 1 (it is bonded only to hydrogen).

The number of electrons surrounding it is 6. (because there is only one bond).

So, the formal charge is:

7 - 1 - 6 = 0.