Answer is: the highest concentration has ⁺H₃NCH(CH₃)CO₂⁻.
pKa(carboxylic group) = -log(4,5·10⁻³) = 2,35.
pKb(amino group) = -log(7,4·10⁻⁵) = 4,13.
pKa + pKb = 14.
pKa(amino group) = 14 - 4,13 = 9,87.
At pH = 7 carboxylic group lost proton(H⁺) and became COO⁻, amine is protoneted (NH₃⁺) in this pH value.
