identify a pH value between 2.5 and 7.5 at which the concentration of the weak acid being titrated is less than the concentration of its conjugate base.

Hello your question is incomplete attached below

A student titrated 50.0mL of a 0.10M solution of a certain weak acid with NaOH(aq). The results are given in the graph above.

answer : pH   > 3.5

Explanation:

During the titration before the equivalence point the solution will behave as a buffer system of a weak acid and base ( conjugated )

when pH ~ pka  the concentration of weak acid = base ( conjugated ) hence when the pH value crosses the pka value , the concentration of the pH value will drop lower than the value of the conjugated base

hence the pH value ≥ 3.5

c (diamond),

sio2 (quartz)