Sodium dithionite, Na2S2O4\text{Na}_2\text{S}_2\text{O}_4Na2S2O4, is a powerful reducing agent used industrially in vat dyeing processes to reduce water-insoluble dyes like indigo into their soluble forms. What is the oxidation number of sulfur in sodium dithionite?
+4+4+4
+5+5+5
+3+3+3
+6+6+6
