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

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

A) 1.66 × 10⁴
B) 9.71
C) 1.92 × 10^{- 10}
D) 5.22 × 10^{- 5}
E) 4.28