When proteins are heated with concentrated $HNO_3$,a yellow color is obtained. What is this test called?

Identify the basic $\alpha$-amino acid from the following.

Amide group is present in

Haemoglobin is

The secondary structure of a protein refers to

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 $(HNO_2)$.