Which one of the following structures represents the peptide chain?

Assertion $(A)$: In aqueous solution,amino acids exist in dipolar ion form.
Reason $(R)$: Most of the naturally occurring amino acids have $L$-configuration.
The correct option among the following is:

$A$ codon has a sequence of $\underline{A}$,and specifies a particular $\underline{B}$ that is to be incorporated into a $\underline{C}$. What are $\underline{A}, \underline{B}, \underline{C}$?
$\underline{A} \quad \underline{B} \quad \underline{C}$

The non-essential amino acid among the following is

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 $N_2$.

The acid showing salt-like character in aqueous solution is