Question - A teacher demonstrated the possible effects of acid rain by placing several types of rocks in separate beakers containing

A teacher demonstrated the possible effects of acid rain by placing several types of rocks in separate beakers containing a vinegar solution with a pH of 3. As time passed, some of the solutions retained a pH of 3 while other solutions gradually reached a pH of 7. Which of the following best explains this variation of pH in this demonstration? 

A) All solutions eventually reach a pH of 7, so the experiment is not complete. 

B) Vinegar is an organic compound that reacts unpredictably with inorganic rocks. 

C) The rocks have varying chemical composition, so some but not all of them react with acid. 

D) The students should have measured the pH immediately after mixing since acid rain reacts quickly in nature.

ANSWER:

C) The rocks have varying chemical composition, so some but not all of them react with acid.