Which of the following does not belong to the vitamin $B$ group?

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

Column $X$	Column $Y$
$(1)$ Skin color	$(P)$ Immunoglobulin
$(2)$ Immunity	$(Q)$ $Mg^{+2}$ containing protein
$(3)$ Movement	$(R)$ Melanin
$(4)$ Exoskeleton	$(S)$ Protein with four heme groups
$(5)$ Photosynthesis	$(T)$ Keratin
$(6)$ Transport of respiratory gases	$(U)$ Globular protein

Which of the following vitamins is water-soluble as well as an antioxidant?

The figure shows a hypothetical tetrapeptide portion of a protein with parts labelled $a$ to $d$. Which one of the following options is correct?

Which nitrogenous base is represented by the given structure?

Match the following structures with their names and select the correct option.