What is the [OH⁻] concentration in an aqueous solution at 25 °C if the H⁺ concentration is 5.5 × 10⁻⁶?
a) 1.82 × 10⁻⁹
b) 1.82 × 10⁻⁵
c) 1.82 × 10⁻⁷
d) 1.82 × 10⁻³