The pH scale is a logarithmic scale used to specify the acidity or basicity of an aqueous solution. It is defined by the formula pH = -log₁₀[H⁺], where [H⁺] is the molar concentration of hydrogen ions. If the pH changes from 3 to 6: At pH 3, -log₁₀[H⁺]₁ = 3, which means log₁₀[H⁺]₁ = -3, so [H⁺]₁ = 10⁻³ M. At pH 6, -log₁₀[H⁺]₂ = 6, which means log₁₀[H⁺]₂ = -6, so [H⁺]₂ = 10⁻⁶ M. Comparing the two concentrations: [H⁺]₂ / [H⁺]₁ = 10⁻⁶ M / 10⁻³ M = 10⁽⁻⁶⁻⁽⁻³⁾⁾ = 10⁻³ = 1/1000. This means the new concentration ([H⁺]₂) is 1/1000 times the original concentration ([H⁺]₁). Therefore, the H⁺ ion concentration decreases 1000 times.