1) Reducing agent 
The dithionite anion ([S2O4]2−), is an oxoanion of sulfur formally derived from dithionous acid, H2S2O4. ==Chemistry== Dithionous acid has not been detected either as a pure compound or in solution. Dithionite ions undergo both acid and alkaline hydrolysis to thiosulfate and bisulfite, and sulfite and sulfide, respectively ==Uses== The sodium sa...
<chemical> Dithionite. The dithionous acid ion and its salts. ... Chemical name: Dithionite ... (12 Dec 1998) ... 
Hydrosulfite