Here's what we can say about the proportion of hydrogen ions (H+) and hydroxide ions (OH-) in a solution with a pH of 4:

* pH 4 is acidic: A pH of 4 indicates an acidic solution.

* Hydrogen ions dominate: In acidic solutions, the concentration of hydrogen ions (H+) is higher than the concentration of hydroxide ions (OH-).

* The relationship is logarithmic: The pH scale is logarithmic, meaning each whole number change in pH represents a tenfold change in the concentration of H+ ions.

* Calculation: Since the pH is 4, the concentration of H+ ions is 10^-4 moles per liter. We can find the concentration of OH- ions using the following relationship (at 25°C):

* Kw (ion product constant for water) = [H+][OH-] = 10^-14

* [OH-] = Kw / [H+] = 10^-14 / 10^-4 = 10^-10 moles per liter

In summary:

* A solution with pH 4 has a much higher concentration of hydrogen ions (10^-4 M) compared to hydroxide ions (10^-10 M).

* The ratio of H+ to OH- ions is 10,000 to 1.