Answer:
A solution that is 0.10 M HC2H3O2 and 0.10 M LiC2H3O2 is a good buffer system.
Step-by-step explanation:
A buffer is defined as the mixture between a weak acid and its conjugate base or vice versa.
For the solutions:
0.10 M HF and 0.10 M LiC2H3O2. HF is a weak acid but LiC2H3O2 is the conjugate base of the weak acid (HC2H3O2, acetic acid).
0.10 M HC2H3O2 and 0.10 M LiC2H3O2. Here, you have a mixture of HC2H3O2, acetic acid, weak acid, and LiC2H3O2 is its conjugate base. Thus, this is a good buffer system
0.10 M LiOH and 0.10 M KOH. LiOH ans KOH are both strong bases.
0.10 M HF and 0.10 M NH4+. Again, HF is a weak acid but NH4+ is the conjugate acid of a weak base (NH3).