The end product of protein digestion is

The correct structure of histidine in a strongly acidic solution $(pH = 2)$ is

The incorrect statement about denaturation of proteins is

In an oligopeptide named Alanyl-glycyl-phenyl-alanyl-isoleucine,the number of $sp^2$ hybridised carbons is $...........$.

Read the following statements carefully:
$(A)$ Albumin is a simple protein.
$(B)$ The amino acid alanine contains an acidic side chain.
$(C)$ Insulin is a hormone.
$(D)$ Muscles contain the protein keratin.
Point out the wrong statements in the above set of statements.

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