For the accompanying fully-protonated amino acid,what is the arrangement of pK_a values in order of increasing magnitude?

Question

Quizplus · Accepted Answer

The pKa values of the amino acid are: 
pKa1 (carboxyl group) = 2;
pKa2 (amino group) = 9;
pKaR (side chain) = variable, depending on the amino acid.
In a fully-protonated form, all groups are positively charged, and the order of increasing magnitude of pKa values will be the opposite of the order of increasing acidity. Acidity increases with decreasing pKa value. 
So, the order of increasing pKa values for the fully-protonated amino acid will be III (side chain) < I (carboxyl group) < II (amino group). 
Therefore, the correct choice is C: III < I < II.

For the Accompanying Fully-Protonated Amino Acid,what Is the Arrangement of PKa

For the Accompanying Fully-Protonated Amino Acid,what Is the Arrangement of PK_a