Which of the following is used in our body as a fuel for muscles and nerves and to build and repair body tissues?

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.

The monomer of a polypeptide is........

The correct zwitter ion structure of glycine is

In the given reaction: $CH_3-CHCl-COOH \xrightarrow[(ii) H_2O]{(i) NH_3 (1 \text{ mole})} [X]$. Product $[X]$ will be:

Identify the essential amino acids from the following:
$A$) Leucine
$B$) Tyrosine
$C$) Cysteine
$D$) Histidine