Which among the following amino acids is $NOT$ synthesized in our body?

Given below are two statements,one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: $A$ solution of the product obtained by heating a mole of glycine with a mole of chlorine in the presence of red phosphorus generates a chiral carbon atom.
Reason $R$: $A$ molecule with $2$ chiral carbons is always optically active.
In the light of the above statements,choose the correct answer from the options given below:

Which of the following statements is/are true for amino acids?
$(A)$ The solubility of an amino acid in water is maximum at its isoelectric point $(pH)$.
$(B)$ It gives a ninhydrin test.
$(C)$ It releases nitrogen gas upon reaction with nitrous acid $(HNO_2)$.

Peptides are:

In $\text{alanyl-glycyl-leucyl-alanyl-valine}$,the number of peptide linkages is $......$

Which is an essential constituent of diet?