Class 12th
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a year agoContributor-Level 10
40. Option (i) Cl-ion form fcc lattice and Na+ ions occupy all octahedral voids of the unit cell is correct since In NaCl, chloride ion form fcc lattice and sodium ions occupy all the octahedral voids of the unit cell. The coordination number of both the cation and anion is found to be 6.
New answer posted
a year agoContributor-Level 10
39. Option (iv) since in this arrangement the spheres of fourth layer are exactly aligned with those of the first layer is correct since in hexagonal close packed structure there is ABAB.type arrangement which means that in this case spheres of third layer are exactly aligned with that of the first layer. Hence, the pattern of spheres is repeated in alternate layers. Thus, the statement at (iv) is not true about hexagonal close packing.
New answer posted
a year agoContributor-Level 10
38. Option (iii) 32 is correct since the packing efficiency in bcc arrangement is 68%, therefore the percentage empty space can be calculated as – 100 - 68 = 32
New answer posted
a year agoContributor-Level 10
37. Option (ii) hcp and ccp is correct since in hcp and ccp the packing efficiency is 74% ( maximum ), hence this pair of packing is considered as the most efficient packing.
New answer posted
a year agoContributor-Level 10
36. Option (i) (A) and (B) is correct since AgBr shows both Frenkel as well as Schottky defects.
New answer posted
a year agoContributor-Level 10
20. Option (i)
Explanation: 2H2O + Cl−→2OH− + H2 + Cl2
The ΔG? is +422 kJ for this reaction. We get ΔE? = −2.2 V, when we convert it to ΔE? (using G? = E? F). It will, of course, require an external e.m.f. greater than 2.2 V. However, electrolysis necessitates an excess potential in order to overcome some other impeding reactions. Thus, Cl2 is obtained through electrolysis, which produces H2 and aqueous NaOH as byproducts. In addition, molten NaCl is electrolyzed. However, in that case, Na metal is formed rat
New answer posted
a year agoContributor-Level 10
19. The metal gold is a nonreactive metal. It is found as a native metal in its free state.
So, it is not compulsory to separate it by a chemical process. Thus, gold is leached to get it in its pure form. In the metallurgy of gold (Au), the respective metal is leached with a dilute mixture of NaCN or KCN in the presence of air where Gold (Au) is oxidized by oxygen of the air to Au+cation which then merges with ions to form a soluble compound.
4Au (s)+8CN− (aq)+O2− (g)+2H2O− (aq)→4 [Au (CN)2]− (aq)+4OH− (aq)
Gold is then obtained from this soluble compound x by replacement method by using a much more electropositive Z
New answer posted
a year agoContributor-Level 10
18. The two import requirements for performing the Vapor Phase Refining Method:
a) The metal which is to be refined should form a volatile compound with an available reagent.
b) The volatile compound formed must be easily decomposable so that it is easy to recover the desired metal.
New answer posted
a year agoContributor-Level 10
17. The chemical reactions taking place in Blast furnace in the temperature range 500-800 K are:
3Fe2O3 + CO→ 2Fe3O4 + CO2
Fe3O4 + 4CO→ 3Fe + 4CO2
Fe2O3 + CO→ 2FeO + CO2
New answer posted
a year agoContributor-Level 10
16. Semiconducting metal is produced by the zone refining method.
Zone refining is centered on the principle that the impurities which are included in the metal ores are more soluble in the molten state as compared to the solid-state of metals.
Zone refining is mostly used for obtaining semiconductor and other metals which are highly pure, e.g., germanium, silicon, etc.
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