Percentage of silver in German silver is (in $\%$)

The correct statement$(s)$ related to the metal extraction processes is(are):
$(A)$ $A$ mixture of $PbS$ and $PbO$ undergoes self-reduction to produce $Pb$ and $SO_2$.
$(B)$ In the extraction process of copper from copper pyrites,silica is added to produce copper silicate.
$(C)$ Partial oxidation of sulphide ore of copper by roasting,followed by self-reduction produces blister copper.
$(D)$ In the cyanide process,zinc powder is utilized to precipitate gold from $Na[Au(CN)_2]$.

Which of the following are the by-products $NOT$ obtained in the extraction of copper?

Gun metal is an alloy of

Give the correct order of initials $T$ or $F$ for following statements. Use $T$ if statement is true and $F$ if it is false.
$(i)$ Every mineral is an ore but every ore is not a mineral.
$(ii)$ Slag is a product formed during the extraction of metal by the combination of flux and impurities.
$(iii)$ Highly pure metals can be obtained by zone refining.
$(iv)$ Carnallite is an ore of magnesium and sodium.

Which of the following is correct?