Which of the following is not an amino acid?

When dilute $H_2SO_4$ is added to an alkaline solution of protein,a violet color is obtained. What is this test called?

Which of the following is manufactured from molecular nitrogen by bacteria?

What type of bonding helps in stabilising the $\alpha$-helix structure of proteins?

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:

Which of the following is a basic amino acid?