What does the concentration of the benzoic acid in the original liquid and the extracting liquid relate to after the extraction is completed?

Answer a. The density of the original liquid.

b. The density of the extracting liquid.

c. The solubility of benzoic acid in each liquid.

d. The melting point of the benzoic acid compared to each liquids boiling point.

Frankly you could have given enough information to help answer your question; I'm guessing the answer is c.

That's what extraction is all about.

The concentration of the benzoic acid in the original liquid and the extracting liquid relates to the solubility of benzoic acid in each liquid after the extraction is completed.

Explanation:
After performing an extraction, the benzoic acid will be dissolved in either the original liquid or the extracting liquid, depending on its solubility. If the benzoic acid is soluble in the original liquid, then the concentration of benzoic acid in the original liquid will decrease after the extraction. On the other hand, if the benzoic acid is soluble in the extracting liquid, then the concentration of benzoic acid in the extracting liquid will increase after the extraction.

Therefore, the relationship between the concentration of benzoic acid in the original liquid and the extracting liquid is determined by the solubility of benzoic acid in each liquid. So, the correct answer is c. The solubility of benzoic acid in each liquid.