Stability of $\alpha$-Helix structure of proteins depends upon:

Within the list shown below,the correct pair of structures of alanine in $pH$ ranges $2-4$ and $9-11$ is:
$I$. $H_{3}N^{+}CH(CH_{3})COOH$
$II$. $H_{2}NCH(CH_{3})COO^{-}$
$III$. $H_{3}N^{+}CH(CH_{3})COO^{-}$
$IV$. $H_{2}NCH(CH_{3})COOH$

Which structure of protein remains intact after coagulation of egg white on boiling?

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

Which of the following statements about proteins is not true?

Differentiate between globular and fibrous proteins.