Assign $A, B, C, D$ from the given type of reaction: $2NaNO_3 + H_2SO_4(conc.) \xrightarrow{Hot} Na_2SO_4 + 2NO_2 + \frac{1}{2}O_2 + H_2O$. (Note: The reaction is a thermal decomposition redox reaction).

$KMnO_4$ oxidises $C_2H_2O_4$ to form $CO_2$. In which of the following,the reaction will be faster?

Identify the substance oxidised,reduced,oxidising agent,and reducing agent for each of the following reactions:
$(a)$ $2 AgBr_{(s)} + C_6 H_6 O_{2(aq)} \rightarrow 2 Ag_{(s)} + 2 HBr_{(aq)} + C_6 H_4 O_{2(aq)}$
$(b)$ $HCHO_{(l)} + 2 [Ag(NH_3)_2]^+_{(aq)} + 3 OH^-_{(aq)}$ $\rightarrow 2 Ag_{(s)} + HCOO^-_{(aq)} + 4 NH_{3(aq)} + 2 H_2 O_{(l)}$
$(c)$ $HCHO_{(l)} + 2 Cu^{2+}_{(aq)} + 5 OH^-_{(aq)} \rightarrow Cu_2 O_{(s)} + HCOO^-_{(aq)} + 3 H_2 O_{(l)}$
$(d)$ $N_2 H_{4(l)} + 2 H_2 O_{2(l)} \rightarrow N_{2(g)} + 4 H_2 O_{(l)}$
$(e)$ $Pb_{(s)} + PbO_{2(s)} + 2 H_2 SO_{4(aq)} \rightarrow 2 PbSO_{4(s)} + 2 H_2 O_{(l)}$

Blue colouration is not produced when :

$KMnO_4$ acts as an oxidizing agent in weak alkaline medium. When weak alkaline $KMnO_4$ is treated with $KI$,iodide ion is oxidized to $.........$

Whenever a reaction between an oxidising agent and a reducing agent is carried out,a compound of lower oxidation state is formed if the reducing agent is in excess and a compound of higher oxidation state is formed if the oxidising agent is in excess. Justify this statement giving three illustrations.