Answer
$a)$ Structure at pH 7;
$b)$electrostatic interaction between the carboxylate and Anion and the protonated amino group of the alanine zwitterion favor the ionization of the carboxyl group. This favourable electrostatic interaction decreases as the length of the Poly (Ala) increases, resulting in an increase in $pK_{1}$.
$c)$ Ionization of the protonated amino group destroys the favourable electrostatic interactions noted in (b). With increasing distance between the charged groups, removal of the proton from the amino group in Poly (Ala). becomes easier and thus $pK_{2}$ is lower. The intramolecular effects of the amide peptide Bond linkages cause the pk value to be lower then they would be for an alkyl-substituted amine.
Work Step by Step
Above is the brief comparing the pKa Values of Alanine and Polyalanine.
