Which amino acid has an imidazole ring?

Which of the following statement$(s)$ is/are true?
$(i)$ All amino acids contain one chiral centre.
$(ii)$ Some amino acids contain one, while some contain more chiral centres or even no chiral centre.
$(iii)$ All amino acids in proteins have $L$-configuration.
$(iv)$ All amino acids found in proteins have $1^{\circ}$ amino group.

Proteins mainly contain:

Biological diversity of amino acids is due to the presence of . . . . . . .

How many polypeptide chains are present in a single molecule of globin protein?

What is formed when two identical or different amino acid units are joined together?