Complex sentence: The hydroxymethanesulfinate ion is unstable in solution towards decomposition to formaldehyde and sulfoxylate ion, however addition of at least one equivalent of formaldehyde pushes the equilibrium towards the side of the adduct and reacts further to give the "bis"-(hydroxymethyl) sulfone.
Split into simpler sentences: The hydroxymethanesulfinate ion is unstable in solution towards decomposition to formaldehyde and sulfoxylate ion. Addition of at least one equivalent of formaldehyde pushes the equilibrium towards the side of the adduct and reacts further to give the "bis"-(hydroxymethyl) sulfone.