Assign $A, B, C, D$ from the given type of reaction.
$Hg(NO_3)_2 + NH_3(soln.) \longrightarrow HgO \cdot HgNH_2NO_3 \downarrow $

Which one of the following conversions does not involve either oxidation or reduction?

$A$ solution of $10 \ mL$ of $\frac{M}{10} \ FeSO_4$ was titrated with $KMnO_4$ solution in an acidic medium. The amount of $KMnO_4$ used will be:

Identify the substance oxidised,reduced,oxidising agent,and reducing agent for each of the following reactions:
$(a)$ $2AgBr_{(s)} + C_6H_6O_{2(aq)} \to 2Ag_{(s)} + 2HBr_{(aq)} + C_6H_4O_{2(aq)}$
$(b)$ $HCHO_{(l)} + 2[Ag(NH_3)_2]^+_{(aq)} + 3OH^-_{(aq)} \to 2Ag_{(s)} + HCOO^-_{(aq)} + 2NH_{3(aq)} + 2H_2O_{(l)}$
$(c)$ $HCHO_{(l)} + 2Cu^{2+}_{(aq)} + 5OH^-_{(aq)} \to Cu_2O_{(s)} + HCOO^-_{(aq)} + 3H_2O_{(l)}$
$(d)$ $N_2H_{4(l)} + 2H_2O_{2(l)} \to N_{2(g)} + 4H_2O_{(l)}$
$(e)$ $Pb_{(s)} + PbO_{2(s)} + 2H_2SO_{4(aq)} \to 2PbSO_{4(s)} + 2H_2O_{(l)}$

$AgCl$ on fusion with $Na_2CO_3$ forms

$HNO_2$ acts as