In neutral or faintly alkaline solution,$8$ moles of permanganate anion quantitatively oxidize thiosulphate anions to produce $X$ moles of a sulphur containing product. The magnitude of $X$ is

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

In neutral or alkaline solution,$MnO_{4}^{-}$ oxidises thiosulphate to.

Justify that the reaction:
$2 Cu_{2}O_{(s)} + Cu_{2}S_{(s)} \rightarrow 6 Cu_{(s)} + SO_{2(g)}$
is a redox reaction. Identify the species oxidised/reduced,which acts as an oxidant and which acts as a reductant.

Which of the following reactions involves oxidation-reduction?

Assign $A, B, C, D$ from the given type of reaction.
$Na_2CO_3 + PbSO_4 \longrightarrow PbCO_3 \downarrow + Na_2SO_4$