What Is the Hydronium Ion Concentration of Pure Water at 25°C

What is the hydronium ion concentration of pure water at 25°C?

A) 7.0 × 10⁷ M
B) 7.0 × 10⁻⁷ M
C) 1.0 × 10⁷ M
D) 1.0 × 10^{−7 M}
E) 1.0 × 10^{−14 M}