Out of the following,which type of interaction is responsible for the stabilisation of $\alpha$-helix structure of proteins?

$\alpha$-$helix$ is a secondary structure of proteins formed by twisting of polypeptide chain into right-handed screw-like structures. Which type of interactions are responsible for making the $\alpha$-$helix$ structure stable?

Coagulation of egg white on boiling is an example of denaturation of protein. Explain it in terms of structural changes.

$A$ zwitter ion is

Sanger's reagent is used for the identification of which of the following?

Identify the basic $\alpha$-amino acid from the following.