Correct Answer - 5
`Na_(2)S_(4)O_(6)` is a salt of `H_(2)S_(4)O_(6)` which has the following structure
`HO-underset(O)underset(||)overset(O)overset(||)S-Soverset((0))-S-underset(O)underset(||)overset(O)overset(||)(S)overset((v))-OH`
`rArr` Difference in oxidation number of two types of sulphur `=5`
