Which of the following amino acids contains the $HN=C(NH_2)-$ linkage?

$A$ tetrapeptide is made of naturally occurring alanine,serine,glycine,and valine. If the $C$-terminal amino acid is alanine and the $N$-terminal amino acid is chiral,the number of possible sequences of the tetrapeptide is $....$

If the side chain group $-R$ for an amino acid is $-CH_{2}OH$,identify the amino acid from the following:

Insulin is a .........

There are $20$ naturally occurring amino acids. The maximum number of tripeptides that can be obtained is

Which among the following $\alpha$-amino acids does $NOT$ have a chiral carbon atom?