The molecular formula of dithionous acid is

Sulfur oxoacid dithionous acid has the chemical formula ${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_4$. Although in pure form it is unstable, its salts, or dithionites, are stable. Using ab initio calculations, it was first believed that the ${\mathrm{C}}_2$ symmetric structure $\mathrm{HOS}-\mathrm{SOH}$is the most stable among molecules with the formula ${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_4$.
Indication: ${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_4$