In pure water, the concentration of hydrogen ions (H⁺) is 1.0 × 10⁻⁷ mol/L. This is because pure water undergoes self-ionization to produce an equal concentration of H⁺ and hydroxide ions (OH⁻), resulting in a neutral pH of 7.
Therefore, the correct option is:
1.0 × 10⁻⁷ mol/L.