The lower the ph of a solution, the a. less toxic the solution b. higher the oh- concentration c. greater the number of oxygen atoms d. more acidic the solution

PH is a measure of the concentration of H+ ions are free in solution. It is defined as pH = -log([H+]). 

If you replace pH with y and [H+] with x, you get the function y = log(x). If you analyze how this function changes as you increase x, this will show you how pH varies as X changes. Remember, H+ makes a solution more acidic!

The answer is d.potassium

There are no metaphors.