$\begin{align}
2C{{H}_{3}}I+2Na\underset{\text{ether}}{\mathop{\xrightarrow{\text{dry}}}}\,{{C}_{2}}{{H}_{6}}+2NaI \\
{{C}_{2}}{{H}_{5}}Cl+2H\xrightarrow{LiAl{{H}_{4}}}{{C}_{2}}{{H}_{6}}+HCl \\
\end{align}$
$(I)$ $CrO_4^{2-}$
$(II)$ $MnO_4^-$
$(III)$ $Cr_2O_7^{2-}$ ?
$(1)$ $\begin{matrix}
O\,\,\,\,\,\,\,\,\,\,\, \\
||\,\,\,\,\,\,\,\,\,\,\,\, \\
{{H}_{3}}C-C-C{{H}_{2}}-Cl \\
\end{matrix}$
$(2)$ ${{H}_{2}}C-C{{H}_{2}}-C{{H}_{2}}-Cl$
$(3)$ ${{({{H}_{3}}C)}_{3}}C-Cl$
$C{H_3}Cl\,\,\xrightarrow{{KCN}}\,\,(A)\,\,\xrightarrow{{{H_2}{O^ + }}}\,\,(B)\,\,\xrightarrow{{N{H_3}}}\,\,(C)\,\,\xrightarrow{\Delta }\,\,(D)$