Final answer:
The protonated amino group of an amino acid will lose a proton when the pH approaches a value more basic than its pKa, around pH 14. A pH significantly above the pKa favors the loss of a proton from the amino group.
Step-by-step explanation:
The protonated amino group of an amino acid will most likely lose a proton as the pH approaches a value higher than its pKa, which is typically around 9 to 10 for the amino group’s conjugate acid. Therefore, as the pH reaches a significantly higher value, such as around 14, the likelihood of a proton being lost from the amino group increases.
Considering the pH scale where 7 is neutral, lower numbers are more acidic, and higher numbers are more basic, the deprotonation of the –NH3⁺ group (the protonated form) to form –NH2 will predominantly occur at a basic pH, rather than an acidic or neutral pH. This means that at a pH of 14, which is highly basic, the protonated amino group is most likely to lose its proton.
Based on the provided pKa values, and considering that acids lose their proton in a medium with a pH above their pKa, option 3) pH 14 is the most probable pH at which the protonated amino group would lose a proton.