Which of the following correctly lists the compounds in order of increasing acidity?

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Correct Answer: C. 
In order of increasing acidity:
ethane (pKa 42) < acetaldehyde (pKa 17) < ethanol (pKa 16) < water (pKa 15.7) < acetic acid (pKa 5)
Note: You did not need the pKa values to solve this question. It is asking you to organize the functional groups from most basic to most acidic. Acetic acid would be the most acidic, and ethane being the most basic (since it lacks an O-H bond). Ethanol and aldehydes are more basic than water, so C is our answer.
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