The value of $x$ in the partial redox equation $MnO_4^- + 8H^{+} + xe^- \rightleftharpoons Mn^{2+} + 4H_2O$ is

Balance the following redox reactions using the oxidation number and ion-electron method:
$(1) H_2S + Fe^{3+} \to Fe^{2+} + S + H^{+}$
$(2) Cu + NO_3^{-} \to Cu^{2+} + NO_2$
$(3) Sn + NO_3^{-} + H^{+} \to Sn^{2+} + NH_4^{+} + H_2O$
$(4) As + NO_3^{-} + H^{+} \to AsO_4^{3-} + NO_2 + H_2O$

What is the value of $x$ and $y$ in order to balance the following redox reaction?
$x CuO + y NH_3 \longrightarrow x Cu + N_2 + x H_2 O$

In acidic medium,potassium dichromate acts as an oxidant according to the equation,$Cr_2O_7^{2-} + 14H^{+} + 6e^- \to 2Cr^{3+} + 7H_2O$. What is the equivalent weight of $K_2Cr_2O_7$? (Molecular weight $= M$)

If the molecular weights of $Na_2S_2O_3$ and $I_2$ are $M_1$ and $M_2$ respectively,then what will be the equivalent weights of $Na_2S_2O_3$ and $I_2$ in the following reaction?
$2S_2O_3^{2-} + I_2 \longrightarrow S_4O_6^{2-} + 2I^-$

The oxidation state of chromium in the final product formed by the reaction between $KI$ and acidified potassium dichromate solution is