Cigarette or gas lighter is made up of

$A$ violet compound of manganese $(A)$ decomposes on heating to liberate oxygen and compounds $(B)$ and $(C)$ of manganese are formed. Compound $(C)$ reacts with $KOH$ in the presence of potassium nitrate to give compound $(B)$. On heating compound $(C)$ with conc. $H_{2}SO_{4}$ and $NaCl$,chlorine gas is liberated and a compound $(D)$ of manganese along with other products is formed. Identify compounds $A$ to $D$ and also explain the reactions involved.

Fill in the blanks:
$1.$ The copper layer on copper coins in the $UK$ is .......... .
$2.$ Copper-silver coins in the $UK$ are an alloy of ............ .
$3.$ The catalyst used for the oxidation of $SO_2$ to $SO_3$ is ......... .

Chromite ore $\xrightarrow{Na_2CO_3 + O_2} A$ $\xrightarrow[NaOH]{H_2SO_4} B$. Which of the following is correct?

The color of $KMnO_4$ is due to:

What is the use of potassium permanganate $(KMnO_4)$?