MCAT General Chemistry Question 287: Answer and Explanation

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Question: 287

6. A stalagmite in a cave suffers damage and researchers want it repaired naturally as quickly as possible. Which of the following will help this process?

A. Adding CaCl₂ to groundwater.
B. Adding chemical compounds in the cave that absorb CO₂ from the air.
C. Increasing the pH of the groundwater supply.
D. Spraying the stalagmite with compressed CO₂.

Correct Answer: B

Explanation:

B According to the passage, increasing the amount of dissolved CaCO₃ that makes it to the ground/cave interface or maximizing the difference in ground and cave CO₂ levels will increase stalagmite formation. Choice A would decrease CaCO₃ solubility in groundwater by the common ion effect. Choice C would decrease CaCO₃ solubility in groundwater because the passage states acidic solutions dissolve CaCO₃. Choices B and D are opposite answers, which often means one is correct. The passage states that lower CO₂ levels in the cave compared to the leaking water lead to precipitation of CaCO₃. Therefore, choice D is eliminated and choice B is the best answer.

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