Explanation

(a)
The important ore of tin is cassiterite $(SnO_{2})$. Tin is extracted from cassiterite ore by carbon reduction method in a blast furnace.
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ SnO_{2} + 2C \rightarrow Sn + 2CO$
The product often contain traces of iron which is removed by blowing air through the melt to oxidise to FeO which then floats to the surface.
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 2Fe + O_{2} \rightarrow 2FeO$.