$A$ piece of steel is heated until redness and then plunged into cold water or oil. This treatment of iron makes it:

Railway wagon axles are made by heating rods of iron embedded in charcoal powder. The process is known as

Extraction of copper from copper pyrite $CuFeS_2$ involves:
$A$. Crushing followed by concentration of the ore by froth-flotation
$B$. Removal of iron as slag
$C$. Self-reduction step to produce 'blister copper' following evolution of $SO_2$
$D$. Refining of 'blister copper' by carbon reduction

Which of the following statements is not correct?

Identify the correct statements from the following:
$I$. Brass is an alloy of copper and nickel
$II$. Bronze is an alloy of copper and zinc
$III$. German silver is an alloy of copper,zinc and nickel
$IV$. Brass is an alloy of copper and zinc

In which of the following metals extraction,impurities are removed as slag?
$i.$ $Al$ $\quad$ $ii.$ $Fe$
$iii.$ $Cu$ $\quad$ $iv.$ $Zn$
The correct option is