Chemistry

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. 

30. Option (iv) ionic solid is correct since in graphite each atom is linked to the other through a covalent bond and hence it is a covalent solid and cannot fall under the category of ionic solid. 

29. Option (iii) electron is correct since lattice sites can only be occupied by electrons when there is imperfection in a solid and do not occur in pure crystals. Hence, the lattice site in a pure crystal cannot be occupied by electrons.

28. Option (iv) CrO₂ is correct since it shows electrical conductivity similar to the metals. 

27. Option (iii) TiO₃  is correct since certain metal oxides such as VO, VO₂, VO₃and TiO₃  show either metallic or insulating properties depending upon the temperature. 

10. Column chromatography is a technique used to separate mixtures based on differences in their affinity towards the stationary phase. If one molecule in a solute has more affinity towards the stationary phase, it would form bonds with the stationary phase and hence remain in the column, Whereas, if the other one has less affinity, it would not form bonds and hence will travel down and come out of the column faster.

As compound A is eluted in preference to compound B, compound B is more readily adsorbed on the column of Al₂O₃.