This is an acid-base reaction (neutralization): H2SO3 is an acid, KOH is a base.
Reactants:



, Lye 
, KOH
, Lye [Potassium hydroxide] 
; Odorless, white or slightly yellow lumps, rods, flakes, sticks, or pellets. [Note: May be used as an aqueous solution.] 
Products: