As the [ H3O+] in a solution decreases, the [ OH - ]

A) Increases and Ph increases

B) Increases and the PH decreases

C) decreases and the PH increases

[H3O+] and [OH-] concentrations are inversely proportional to each other. this means that if the [H3O+] decreases, the [OH-] increases.

Also remember that pH depends on the concentration of [H3O+]. if this concentration increases, the solution is more acidic and the pH decreases.

with this information, we can determine the answer is C

Answer: C) decreases and the pH increases.

Justification:

1) [H₃O⁺] and [OH⁻] in a solution are inversely related as per this equation:

[H₃O] [OH⁻] = 1 * 10⁻¹⁴

That means that if one increases the other has to decrease (to keep the product constant equal to 1 * 10⁻¹⁴).

2) The pH is defined as:

pH = log { 1 / [H₃O⁺] }

As [H₃O⁺] decreases, 1 / [H₃O⁺] increases, so being the logarithmic function a growing function, pH will increase.

That, explains why as [H₃O⁺] decreases the pH increases.

So, the lower the [H₃O⁺], the higher the pH, and the less acidic (more basic) the solution.