The pH of a solution is 9.55 at 25°C. What is the hydroxide-ion concentration in the solution?

a. 2.8 × 10⁻¹⁰ M 

b. 3.5 × 10⁻⁵ M

c. 3.1 × 10⁻¹⁰ M 

d. 3.2 × 10⁻⁵ M

e. 3.8 × 10⁻⁵ M