Question

What the oxidation number of the sufur atom in K2SO4?

Answer 1

We gots `S(VI+)` in potassium sulfate....

Explanation:

As always, the sum of the oxidation numbers EQUALS the charge on the ion or species....here we gots `SO_4^(2-)`...and the oxidation numbers of oxygen is USUALLY `-II` in its compounds, and it is so here...

And thus `4xx-II_"O"+"oxidation number of S"=-2`

And so we add `+VIII` to each side....to get...

`"oxidation number of S"=-2+VIII=VI+`

...i.e. here sulfur is fully oxidized...and its oxidation number is the same as its Group number on the Periodic Table...

What about the oxidation state of sulfur in thiosulfate, i.e. `S_2O_3^(2-)`?