-Refer to Exhibit 3A

$$\begin{array}{l}\text { Exhibit } \mathbf { 3 A } \text { (for this chapter) }\\\begin{array} { l l l l } \text { Amino acid } & \boldsymbol { \alpha } \text {-carboxyl group pK a } & \boldsymbol { \alpha } \text {-amino group pK a } & \text { R-group pK } \\\hline \text { Ala } & 2.3 & 9.7 & \\\text { Arg } & 2.2 & 9.0 & 12.5 \\\text { Asn or Gln } & 2.1 & 9.0 & 4.0 \\\text { Asp or Glu } & 2.2 & 9.8 & 8.3 \\\text { Cys } & 1.7 & 10.8 & 6.0 \\\text { His } & 1.8 & 9.2 & \\\text { Ser } & 2.2 & 9.2 & 10.1\end{array}\end{array}$$
-Refer to Exhibit 3A. Which one has the R-group with the highest pK?

A) Alanine
B) Arginine
C) Histidine
D) Cysteine
E) Aspartic Acid