What is the mathematically calculated average oxidation number of Sulphur in the tetrathionate ion ( — Redox Reactions and Volumetric Analysis Chemistry Question

💡 Solution & Explanation

Mathematically, using standard assignment rules, $4x + 6(-2) = -2 \Rightarrow 4x = 10 \Rightarrow x = +2.5$ . However, the actual physical structure of the tetrathionate ion is a linear chain: $^-O_3S-S-S-SO_3^-$ . The two terminal sulphur atoms are bonded to three highly electronegative oxygens, acquiring a $+5$ oxidation state. The two central sulphur atoms are bonded solely to other identical sulphur atoms via single bonds, leaving their true structural oxidation state at $0$ .