Calculating n factor of SO2
As this is clearly a homework question, I will only point you in the right direction.

Balance the oxidation reaction:

$$\ce{S2^2- -&gt; 2 SO2 + $n$e^-}$$

Balancing the charges will give you $n$. (I'll leave the balancing to the OP, as this is homework).

The equivalent mass of $\ce{SO2}$ in this reaction is then:

$$N=\frac{2M}{n}$$

The factor $2$ is needed because the electronically balanced reaction has two molecules of sulphur dioxide in the equation.