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JEE Advanced 2025 Paper 1 · Chemistry · s-Block, p-Block Elements and Hydrogen · medium

Consider the six anions S2O3^2-, S2O4^2-, S2O5^2-, S2O7^2-, S2O8^2- and S4O6^2- (all in their usual structures: thiosulfate, dithionite, disulfite…

Numerical answer

Consider the six anions S2O32−\mathrm{S_2O_3^{2-}}, S2O42−\mathrm{S_2O_4^{2-}}, S2O52−\mathrm{S_2O_5^{2-}}, S2O72−\mathrm{S_2O_7^{2-}}, S2O82−\mathrm{S_2O_8^{2-}} and S4O62−\mathrm{S_4O_6^{2-}} (all in their usual structures: thiosulfate, dithionite, disulfite, disulfate, peroxodisulfate and tetrathionate). What is the total number of S ⁣− ⁣S\mathrm{S\!-\!S} bonds present in these six ions taken together?
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Answer: 6

Draw each structure. Thiosulfate S ⁣− ⁣SO32−\mathrm{S\!-\!SO_3^{2-}} has one S ⁣− ⁣S\mathrm{S\!-\!S} bond (1). Dithionite O2S ⁣− ⁣SO22−\mathrm{O_2S\!-\!SO_2^{2-}} has one (1). Disulfite O2S ⁣− ⁣SO32−\mathrm{O_2S\!-\!SO_3^{2-}} has one (1). Disulfate (pyrosulfate) O3S ⁣− ⁣O ⁣− ⁣SO32−\mathrm{O_3S\!-\!O\!-\!SO_3^{2-}} has an S ⁣− ⁣O ⁣− ⁣S\mathrm{S\!-\!O\!-\!S} bridge and no S ⁣− ⁣S\mathrm{S\!-\!S} bond (0). Peroxodisulfate O3S ⁣− ⁣O ⁣− ⁣O ⁣− ⁣SO32−\mathrm{O_3S\!-\!O\!-\!O\!-\!SO_3^{2-}} has an O ⁣− ⁣O\mathrm{O\!-\!O} bridge and no S ⁣− ⁣S\mathrm{S\!-\!S} bond (0). Tetrathionate O3S ⁣− ⁣S ⁣− ⁣S ⁣− ⁣SO32−\mathrm{O_3S\!-\!S\!-\!S\!-\!SO_3^{2-}} has a chain of four sulfur atoms, hence three S ⁣− ⁣S\mathrm{S\!-\!S} bonds (3). Total =1+1+1+0+0+3=6=1+1+1+0+0+3=6. Counting only direct sulfur to sulfur links, and not bridging oxygen atoms, is essential here; the peroxo and ether-type bridges contribute nothing to the answer.
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