carbon reduction of an oxide ore
self-reduction of a sulphide ore
removal of copper impurity
removal of iron impurity
Tin is obtained by reducing the ore cassiterite with coal in a reverberatory furnace; Limestone is added to produce a slag with the impurities, which can be separated. SnO2 + 2C → Sn + 2CO Crude tin so obtained is contaminated with iron, copper, lead and other metals. It is, therefore, remelted on an inclined furnace. The process is called liquation. The easily fusible tin melts away and the less fusible impurities are left behind. Molten tin is finally stirred with green poles of wood in contact with air. In this process, any remaining metal impurities are oxidized forming a scum, which rises to the surface and is removed. This process is called poling. Hence, A, C, and D is the answer.