Which is the most abundant protein in the animal kingdom?

Select the correct match for $X$ and $Y$:

Column $X$	Column $Y$
$(1)$ Primary protein	$(P)$ Globular or fibrous form
$(2)$ Secondary protein	$(Q)$ Three-dimensional arrangement of a single polypeptide chain
$(3)$ Tertiary protein	$(R)$ Gene-controlled
$(4)$ Quaternary protein	$(S)$ Helical or pleated sheet form

Which of the following is least likely to be involved in stabilizing the three-dimensional folding of a protein?

What does the part labeled '$X$' represent in the structural formula shown below?

Which of the following is a simple protein?

$S$ - Statement: Hemoglobin is a conjugated protein.
$R$ - Reason: Hemoglobin contains globin protein in its structure.