The concentration of H₃O⁺ ions in pure water at 25°C is correctly represented by the option:
1.0 × 10^-7 mol/L
In pure water, the concentration of hydrogen ions (H₃O⁺) is equal to the concentration of hydroxide ions (OH⁻), and both are \(1.0 \times 10^{-7}\) mol/L, which corresponds to a neutral pH of 7.