$\text{Pyrosulphurous acid }+\text{ Excess NaOH solution}\underset{ }{\overset{ }{\to }}\text{'}\mathrm{P}\text{'}+2{\mathrm{H}}_2\mathrm{O}$

Find the value of expression |x-y| for salt ‘P’,  where x = total number of pi bonds between non metals
and y = maximum number oxygens with double bonds