Class 12th

15. In metallurgical processes, Flux works as various types of agents like chemical agents, cleaning/purifying agents.

Fluxes have many important properties such as corrosivity, cleanability, conductivity, volatility, etc.

Flux, when combined with gangue together, forms slag i.e. Flux + Gangue = Slag

As compared to gangue, slag separates much easily from the ore, in this way the removal of gangue also becomes much easier.

Flux is useful for making the molten mass more conducting which helps to remove impurities from metals through electrolytic metallurgical processes.

35. Option (ii) 8 is correct since in face centred cubic unit cell the number of atoms per unit cell is 4 atoms and hence the number of tetrahedral voids in fcc unit cell is found to be 8

14. The considerations during the extraction of metals by electrochemical method are :

a) Reactivity of metals: If the metals are reactive and are likely to react with water then the metals should be isolated by the electrolysis of their purified molten ore rather than their aqueous solution.

b) Suitability of electrodes:The electrode is carefully chosen so that they should not react with the product of electrolysis. If they react then the electrodes must be made of a material which is quite cheap so their replacement should not increase the cost of the process.

34. Option (iv) 5 is correct since silicon is doped with a pentavalent substance like Phosphorus or Arsenic so, four out of five electrons are used in the formation of four covalent bonds with four of its neighbouring silicon atoms. The fifth electron is extra and becomes delocalised. These delocalised electrons increase the conductivity of doped silicon. 

33. Option (ii) neutral is correct since p-type semiconductor mainly contains positively charged carriers ( holes ) which are able to move freely. It is still considered to be neutral as the fixed acceptor atoms having accepted electrons are negative. 

12. Sulfide ore of copper contains some types of impurities. Sulfide ores are not reduced easily, but oxide ores are easily reduced. It is necessary to make sulfide ores free from volatile impurities. This can be performed by a roasting method. In this moisture escape and impurities like sulfur, phosphorus, arsenic are oxidized to their volatile oxides. It is performed in a reverberatory furnace. After this process the mass becomes porous.

32. Option (ii) equal number of cations and anions are missing from the lattice is correct since Schottky defect in crystals occurs when equal numbers of cations and anions are missing from the lattice.

10. Sulfide ores are not reduced easily, but oxide ores are easily reduced. Sulfide ore of copper contains some types of impurities. This can cause by-product formation and degrade our final product. Iron oxide is present as a key impurity of concern in sulfide ore of copper. During the roasting process the temperature in the furnace is near about 1200°C. During such high temperatures iron oxide which is gangue (impurity) in ore forms slag. Slag is insoluble in molten metal and being lighter floats over the surface of molten metal. Here silica is used as flux.

FeO + SiO₂ →FeSiO₃ 

31. Option (i) Frenkel defect is correct since it is a type of defect in which an atom is dislocated from its lattice position to an interstitial site.