Which of the following electrolyte can be used to obtain $\mathrm{H}_2 \mathrm{~S}_2 \mathrm{O}_8$ by the process of electrolysis ?

Given below are two statements :

Statement I : $\quad \mathrm{CH}_3-\mathrm{O}-\mathrm{CH}_2-\mathrm{Cl}$ will undergo $\mathrm{S}_{\mathrm{N}} 1$ reaction though it is a primary halide.

Statement II : will not undergo $\mathrm{S}_{\mathrm{N}} 2$ reaction very easily though it is a primary halide.

In the light of the above statements, choose the most appropriate answer from the options given below :

The products formed in the following reaction sequence are :

From the magnetic behaviour of $\left[\mathrm{NiCl}_4\right]^{2-}$ (paramagnetic) and $\left[\mathrm{Ni}(\mathrm{CO})_4\right]$ (diamagnetic), choose the correct geometry and oxidation state.