The concentration of H3O+ in a solution is 4 × 10⁻⁴M at 25°C. What is its hydroxide-ion concentration? (Kw = 1.01 × 10⁻¹⁴)
a. 2 × 10⁻¹⁰ M
b. 4 × 10⁻⁴ M
c. 3 × 10⁻¹¹ M
d. 5 × 10⁻¹⁰ M
e. 4 × 10⁻¹⁰ M