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

For the balanced redox reaction $aZn + b \, HNO_3 \to c \, Zn(NO_3)_2 + d \, NH_4NO_3 + 3H_2O$,the value of $b$ is:

In dilute alkaline solution,$MnO_4^-$ changes to:

Observe the following reaction:
$xS_{8\text{(s)}} + yOH^{-}{_{\text{(aq)}}} \rightarrow zS^{2-}{_{\text{(aq)}}} + 2S_2O_3^{2-}{_{\text{(aq)}}} + 6H_2O_{\text{(l)}}$
Find the values of $x, y$ and $z$ respectively.

Which of the following reactions is a redox reaction?

Consider the following redox reaction taking place in acidic medium: $BH_{4}^{-}(aq) + ClO_{3}^{-}(aq) \rightarrow H_{2}BO_{3}^{-}(aq) + Cl^{-}(aq)$. If the Nernst equation for the above balanced reaction is $E_{cell} = E_{cell}^{o} - \frac{RT}{nF} \ln Q$, then the value of $n$ is . . . . . . . (Nearest integer)