Final answer:
The correct acid-conjugate base pair among the options provided is HF and F-, which is option 3. This pair exemplifies an acid (HF) losing a proton to become its conjugate base (F-), consistent with the Brønsted-Lowry theory.
Step-by-step explanation:
The student has asked which pair among the given options is an acid-conjugate base pair. The concept behind this pair is based on the Brønsted-Lowry theory of acids and bases, which states that an acid is a proton (H+) donor and its conjugate base is the species that remains after the proton has been donated.
Therefore, to identify an acid-conjugate base pair, we look for a pair of substances that differ only by the presence or absence of a proton. Now, looking at the provided pairs:
- HF and H2O are not an acid-base pair since they do not differ by just a proton.
- H2O and H3O+ similarly do not form an acid-base pair because H2O is acting as a base here by accepting the proton to form its conjugate acid H3O+.
- HF and F- do form a conjugate acid-base pair. When HF loses a proton, it forms its conjugate base, F-.
- H3O+ and F- are not a pair in this context, as they do not represent an acid losing a proton to form a base.
The correct answer is option 3), HF and F-, as they are a true example of an acid (HF) donating a proton to become its conjugate base (F-).