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Consider the following titration data and the accompanying graph of pH vs. Volume of $NaOH$. The data were obtained when a known mass of a monoprotic weak acid was titrated with a standard sodium hydroxide solution.

Volume of NaOH (mL) pH Volume of NaOH (mL) pH
0.00 2.95 28.00 6.22
10.00 4.48 29.00 7.22
15.00 4.82 30.00 11.18
17.00 4.91 31.00 11.54
19.00 5.09 32.00 11.75
21.00 5.18 33.00 11.88
23.00 5.35 34.00 11.98
25.00 5.58 35.00 12.04
26.00 5.71 40.00 12.25
27.00 5.91 ---- ----

Based on this information, what is the approximate value of ${pK}_{a}$ for this acid?

A

4.8

B

8.4

C

–4.8

D

–8.4

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