Which option correctly shows the concentration of H3O* ions in pure water?

In pure water at 25°C, the concentration of hydronium ions (H₃O⁺) is \(1.0 \times 10^{-7}\) mol/L. This is due to the self-ionization of water, where water dissociates into equal concentrations of H₃O⁺ and OH⁻ ions.

Therefore, the correct option is:
- **1.0 × 10^-7 mol/L**.