In which of the following processes does protein $NOT$ participate?

The correct structure of product $P$ in the following reaction is
$Asn-Ser + (excess) (CH_3CO)_2O \xrightarrow{NEt_3} P$

For $\alpha$-amino acids having the structure $R-CH(NH_2)-CO_2H$,which of the following statements are true?
$(a)$ Water solubility is maximum at a $pH$ when concentrations of anions and cations are equal.
$(b)$ They give ninhydrin test.
$(c)$ On reacting with nitrous acid,they give off $N_2$.

Assertion : Carboxypeptidase is an exopeptidase.
Reason : It cleaves the $N$-terminal bond.

$\alpha$-Amino acids are:

At the isoelectric point: