What does hemoglobin in red blood cells primarily contain?

Which of the following amino acids contains the $HN=C(NH_2)-$ linkage?

Which of the following acids behaves like a salt in aqueous solution?

Observe the structures of the following compounds:
$1$. $2$-chlorobutane
$2$. Glycine $(NH_2CH_2COOH)$
$3$. Alanine $(CH_3CH(NH_2)COOH)$
$4$. Styrene $(C_6H_5CH=CH_2)$
$5$. Menthol
The total number of structures/compounds which possess asymmetric carbon atoms is $....$

The helical structure of protein is stabilized by$-$

In the following compound,the favourable site/s for protonation is/are:
(Image description: Adenine structure with labels $a$ on the exocyclic $-NH_2$ group,$b$ on the pyrimidine ring nitrogen,$c$ on the other pyrimidine ring nitrogen,$d$ on the imidazole ring nitrogen,and $e$ on the imidazole ring $-NH-$ group.)