Final answer:
Only the mixture of HF and NaF and the mixture of HC2H3O2 and KC2H3O2 can form buffer solutions. Mixtures containing strong acids like HCl or strong bases like NaOH do not constitute buffers.
Step-by-step explanation:
To determine whether a mixture is a buffer, it is important to identify if it consists of a weak acid and its conjugate base or a weak base and its conjugate acid. A buffer's key characteristic is its ability to resist changes in pH when small amounts of acid or base are added.
A mixture of HCl (hydrochloric acid) and HF (hydrofluoric acid) is not a buffer because both are acids and HCl is a strong acid, which does not form part of a buffer system. HF and NaF potentially can form a buffer because HF is a weak acid and NaF is a source of fluoride ions, the conjugate base of HF. HC2H3O2 (acetic acid) and KC2H3O2 (potassium acetate) will form a buffer as HC2H3O2 is a weak acid and KC2H3O2 provides the conjugate base, acetate. Lastly, a mixture of NaOH (sodium hydroxide) and NH3 (ammonia) does not constitute a buffer because NaOH is a strong base and it does not pair with a conjugate acid.