How many amino acids are present in insulin?

Which amino acid does not contain a chiral center?

Which of the following statements is $NOT$ correct for amino acids?

Total number of essential amino acids among the given list of amino acids is . . . .
Arginine,Phenylalanine,Aspartic acid,Cysteine,Histidine,Valine,Proline

Assertion $(A)$: An optically active amino acid can exist in three forms depending on the $pH$ of the solution.
Reason $(R)$: Amino acids contain both acidic and basic groups; they exist as a zwitterion in aqueous medium,anionic form in basic medium,and cationic form in acidic medium.

Which is the $C$-terminal residue in glycyl alanine?