Answer:
water
Acidity and basicity are usually determined in a solvent. The strongest acid in the solvent is always the conjugate acid of the solvent and the strongest base is the conjugate base of the solvent. So, in water, the strongest acid is H3O+ and the strongest base is OH- (conjugate base of water).
Do you have a picture of the graph?
Answer:

Explanation:
From the question we are told that:
pKa for Acetic Acid 
Therefore
For Equal Concentration of acetic acid and acetatic ion

Generally the Henderson's equation for pH value is mathematically given by



