What Is the Concentration (In M) of Hydroxide Ions in a Solution

What is the concentration (in M) of hydroxide ions in a solution at 25.0 °C with pH = 4.282?

A) 5.22 × 10^{- 5}
B) 1.91 × 10^{- 10}
C) 9.72
D) 4.28
E) 1.66 × 10⁴