Na₂S₂O₃ is prepared by

(a) ${\mathrm{Na}}_2{\mathrm{SO}}_3+\mathrm{S}\stackrel{ \mathrm{boiling}}{\to }{\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3$; In the laboratory Na₂S₂O₃ is prepared by boiling alkaline (or) neutral sodium sulphite with ‘flowers of sulphur’
(c) Sodiumpentasulphide also converts into hypo when exponed to air $2{\mathrm{Na}}_2{\mathrm{S}}_5+3{\mathrm{O}}_2\stackrel{ \mathrm{heating} \mathrm{in} air}{\to }2{\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3+6\mathrm{S}$
(d) $$\begin{gathered} 6\mathrm{NaOH}+4\mathrm{S}\stackrel{∆}{\to }{\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3+2{\mathrm{Na}}_2\mathrm{S}+3{\mathrm{H}}_2\mathrm{O} \\ 6\mathrm{NaOH} + 12\mathrm{S}\left(\mathrm{excess}\right)\to {\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3+2{\mathrm{Na}}_2{\mathrm{S}}_5+3{\mathrm{H}}_2\mathrm{O} \end{gathered}$$