What does pH measure?
the concentration of oxygen atoms in solution
the total number of acid molecules in solution
the total number of base molecules in solution
the concentration of hydrogen lons in solution

Answer below

Explanation: pH is a measure  of the acidity or alkalinity of a solution. What the pH scale measures is basically the concentration of hydrogen and hydroxyl atoms in a solution. So, the last option is the answer. Another thing to keep in mind is solutions with a pH under 7 are acidic, solutions with a pH of 7 are neutral, and solutions with a pH over 7 are alkaline or considered a base. I hope this helped! Good luck:)

hey there hope i ,

the answer is heat

lichens that colonize bare rock secrete acids that break down the rock and start the soil-production process. so they expose rocks