The HBr is a strong acid, that is, it is fully consumed in the reaction
molar mass HBr = 80.91 g/mol
number of moles = 5.0 x 10⁻⁴ / 80.91 = 6.17 x 10⁻⁶ moles
molarity = 6.17 x 10⁻⁶ / 1.2 = 5.14 x 10⁻⁶ M
HBr ------------------- H₃O⁺ + Br ⁻ ↓ ↓ ↓ 5.14 x 10⁻⁶ 0 0 - 5.14 x 10⁻⁶ 5.14 x 10⁻⁶ 5.14 x 10⁻⁶ _____________________________________ 0 5.14 x 10⁻⁶ M 5.14 x 10⁻⁶ M
