NEET 2020 Botany Question 28 Solution

- (a) Iron ($Fe^{3+}$ / $Fe^{2+}$): Constituent of cytochromes and ferredoxin in electron transport; reversibly oxidized during redox reactions. Although not a structural constituent of the chlorophyll porphyrin ring (which contains $Mg^{2+}$), iron is an indispensable cofactor required for chlorophyll biosynthesis. - (b) Zinc ($Zn^{2+}$): Activates diverse dehydrogenases and carbonic anhydrase; plays an obligatory catalytic role in the enzymatic biosynthesis of auxin (indole-3-acetic acid, IAA) from its amino acid precursor tryptophan. - (c) Boron ($BO_3^{3-}$ / $B_4O_7^{2-}$): Essential for $Ca^{2+}$ uptake and utilization, membrane functioning, cell elongation, carbohydrate translocation via phloem, and pollen germination. - (d) Manganese ($Mn^{2+}$): Best known for its role in the photolysis of water (splitting of water) to evolve molecular oxygen ($O_2$) during light reactions of photosynthesis in Photosystem II.

Matching sequence is: (a)-(iii), (b)-(iv), (c)-(ii), (d)-(i). This corresponds perfectly to Option (3).