General Principles and Processes of Isolation of Elements - MCQs with Explanations

1. Which of the following statements is correct regarding the slag obtained during the extraction of a metal like copper or iron?

• (a) The slag is lighter and has higher melting point than the metal.
• (b) The slag is lighter and has lower melting point than the metal.
• (c) The slag is heavier and has higher melting point than the metal.
• (d) The slag is heavier and has lower melting point than the metal.

Correct Answer: (b)

Explanation: Slag is lighter and has a lower melting point than the metal, allowing it to float on top and be easily skimmed off.

2. In blast furnace, iron oxide is reduced by:

• (a) silica
• (b) carbon monoxide
• (c) carbon dioxide
• (d) limestone.

Correct Answer: (b)

Explanation: In the blast furnace, iron oxide ($Fe_{2}O_{3}$) is reduced to iron by carbon monoxide (CO).

3. The most electropositive metals are obtained from their ores by:

• (a) high temperature reduction with carbon
• (b) electrolytic reduction of their fused ionic salts
• (c) self-reduction
• (d) thermal decomposition.

Correct Answer: (b)

Explanation: Highly electropositive metals like Potassium, Sodium, Calcium, and Magnesium are extracted via the electrolysis of their molten (fused) chlorides.

4. The extraction principle used in extraction of a metal 'M' can be represented as: $MS + 2O_{2} \rightarrow MSO_{4}$; $MSO_{4} + MS \rightarrow 2M + 2SO_{2}$. The metal 'M' is:

• (a) Mg
• (b) Pb
• (c) Sn
• (d) Fe

Correct Answer: (b)

Explanation: This series of reactions represents the self-reduction process used for metals like Lead (Pb).

5. Reduction of a metal oxide by excess carbon at high temperature can be successfully applied in the case of:

• (a) BeO and $Al_{2}O_{3}$
• (b) ZnO and $Fe_{2}O_{3}$
• (c) CaO and $Cr_{2}O_{3}$
• (d) BaO and $U_{3}O_{8}$

Correct Answer: (b)

Explanation: Carbon reduction is effective for extracting moderately reactive metals like Zinc and Iron from their oxides.

6. Silver containing lead as an impurity is purified by:

• (a) poling
• (b) cupellation
• (c) levigation
• (d) distillation.

Correct Answer: (b)

Explanation: Cupellation is used to refine silver when it is contaminated with lead.

7. Which of the following processes is used in the extractive metallurgy of magnesium?

• (a) Fused salt electrolysis
• (b) Self-reduction
• (c) Aqueous solution electrolysis
• (d) Thermite reduction

Correct Answer: (a)

Explanation: Magnesium is extracted by the electrolysis of anhydrous fused $MgCl_{2}$.

8. Which method is not correctly given for refining of crude metals?

• (a) Distillation: Zinc and mercury
• (b) Liquation : Tin
• (c) van Arkel: Zirconium
• (d) Mond's process : Lead

Correct Answer: (d)

Explanation: Mond's process is used for the purification of Nickel, not Lead.

9. The metal used to recover copper from a solution of $CuSO_{4}$ is:

• (a) Fe
• (b) He
• (c) Na
• (d) Ag

Correct Answer: (a)

Explanation: Iron (Fe) is more reactive than copper and can displace it from a $CuSO_{4}$ solution.

10. The major role of fluorspar ($CaF_{2}$) added in the electrolytic reduction of alumina is:

• (a) to make the fused mixture very conducting and lower the melting point
• (b) as a catalyst
• (c) to lower the temperature of melting only
• (d) to decrease the rate of oxidation of carbon at the anode.

Correct Answer: (a)

Explanation: Fluorspar is added to increase the electrical conductivity and decrease the melting point of the alumina-cryolite mixture.

11. The methods chiefly used for the extraction of lead and tin from their ores are respectively:

• (a) self-reduction and carbon reduction
• (b) carbon reduction and self-reduction
• (c) cyanide process and carbon reduction
• (d) none of the above.

Correct Answer: (a)

Explanation: Tin is extracted solely by carbon reduction, while lead can be extracted via self-reduction or carbon reduction.

12. How is impure Ni purified?

• (a) $Ni + CO_{2} \rightarrow NiCO_{3} \rightarrow NiO \rightarrow Ni$
• (b) $Ni + CO \rightarrow Ni(CO)_{6(g)} \rightarrow Ni + CO$
• (c) $Ni + CO \rightarrow Ni(CO)_{4(s)} \rightarrow Ni + CO$
• (d) $Ni + CO \rightarrow Ni(CO)_{4(g)} \rightarrow Ni + CO$

Correct Answer: (d)

Explanation: In Mond's process, impure Nickel is converted into volatile nickel tetracarbonyl gas, which then decomposes to pure metal.

13. In the purification of Zr and B, which of the following is/are true?

• (a) $Zr + 2I_{2} \rightarrow ZrI_{4(g)}$; Pure Zr is deposited on W.
• (b) $2B + 3I_{2} \rightarrow 2BI_{3(g)}$; Pure B is deposited on W.
• (c) $Zr + 2I_{2} \rightarrow ZrI_{4(s)}$. $ZrI_{4}$ is reduced to $ZrI_{2}$.
• (d) Both (a) and (b) are correct.

Correct Answer: (d)

Explanation: Both Zirconium and Boron are purified using the van Arkel method, involving volatile iodide formation and decomposition on a tungsten filament.

14. For which of the given sulphides autoreduction is not applicable?

• (a) $Cu_{2}S$
• (b) PbS
• (c) FeS
• (d) $Sb_{2}S_{3}$

Correct Answer: (c)

Explanation: Autoreduction (self-reduction) is applicable to less electropositive metals like Cu, Pb, and Hg, but not to Iron (Fe).

15. The rocky and silicious matter associated with an ore is called:

• (a) slag
• (b) mineral
• (c) matrix or gangue
• (d) flux.

Correct Answer: (c)

Explanation: Gangue or matrix refers to the earthy/rocky impurities present in an ore.

16. An ore after levigation is found to have basic impurities. Which of the following can be used as a flux?

• (a) MgO
• (b) $CaCO_{3}$
• (c) $SiO_{2}$
• (d) FeO

Correct Answer: (c)

Explanation: $SiO_{2}$ (Silica) is an acidic flux used to remove basic impurities.

17. Aluminium is obtained by:

• (a) reducing $Al_{2}O_{3}$ with coke
• (b) electrolysing $Al_{2}O_{3}$ dissolved in $Na_{3}AlF_{6}$
• (c) reducing $Al_{2}O_{3}$ with chromium
• (d) heating alumina with cryolite.

Correct Answer: (b)

Explanation: Aluminum is extracted through the electrolytic reduction of alumina dissolved in molten cryolite.

18. Impure $Ni + 4CO \xrightarrow{320 K} Ni(CO)_{4} \xrightarrow{420 K} Pure Ni + 4CO$. This method is:

• (a) Cupellation
• (b) Mond's process
• (c) van Arkel method
• (d) Zone refining.

Correct Answer: (b)

Explanation: These reactions specifically define the Mond's process for nickel purification.

19. Roasted gold ore $+ CN^{-} + H_{2}O \xrightarrow{O_{2}} [X] + OH^{-}$; $[X] + Zn \rightarrow [Y] + Au$. [X] and [Y] are:

• (a) $X = [Au(CN)_{2}]^{-}$; $Y = [Zn(CN)_{4}]^{2-}$
• (b) $X = [Au(CN)_{4}]^{3-}$; $Y = [Zn(CN)_{4}]^{2-}$
• (c) $X = [Au(CN)_{2}]^{-}$; $Y = [Zn(CN)_{6}]^{4-}$
• (d) $X = [Au(CN)_{4}]^{3-}$; $Y = [Zn(CN)_{6}]^{4-}$

Correct Answer: (a)

Explanation: Gold forms a dicyanoaurate(I) complex, which is then displaced by zinc to form a tetracyanozincate(II) complex.

20. To separate PbS, ZnS and FeS from each other in froth floatation, reagents are used in which sequence?

• (a) potassium ethyl xanthate, KCN
• (b) potassium ethyl xanthate, KCN, NaOH, $CuSO_{4}$, acid
• (c) KCN, $CuSO_{4}$, acid
• (d) none of these.

Correct Answer: (b)

Explanation: Collectors (xanthate), depressants (KCN/NaOH), and activators ($CuSO_{4}$) are used sequentially to isolate the different sulphide ores.

21. In thermite process, the reducing agent is:

• (a) C
• (b) Zn
• (c) Na
• (d) Al

Correct Answer: (d)

Explanation: Aluminum (Al) powder acts as the reducing agent in the aluminothermic (thermite) process.

22. Native silver metal forms a water soluble complex with dilute NaCN in the presence of:

• (a) nitrogen
• (b) oxygen
• (c) carbon dioxide
• (d) argon.

Correct Answer: (b)

Explanation: Oxygen is required to oxidize the silver in the presence of cyanide ions to form the soluble complex.

23. The method of zone refining of metals is based on the principle of:

• (a) greater mobility of pure metal
• (b) higher melting point of impurity
• (c) greater noble character of metal
• (d) greater solubility of the impurity in the molten state than in the solid.

Correct Answer: (d)

Explanation: Zone refining relies on the fact that impurities are more soluble in the molten zone than in the solidified metal.

24. Match Ni, Cu, Zr, Ga with methods: electrolysis, van Arkel, zone refining, Mond's process.

• (a) Ni: Electrolysis, Cu: van Arkel, Zr: Zone refining, Ga: Mond's
• (b) Ni: Mond's, Cu: Electrolysis, Zr: van Arkel, Ga: Zone refining
• (c) Ni: Mond's, Cu: van Arkel, Zr: Zone refining, Ga: Electrolysis
• (d) Ni: Electrolysis, Cu: Zone refining, Zr: van Arkel, Ga: Mond's

Correct Answer: (b)

Explanation: Standard matches are: Ni (Mond's), Cu (Electrolysis), Zr (van Arkel), and Ga (Zone refining).

25. In electrorefining the impure metal is made:

• (a) anode
• (b) cathode
• (c) anode or cathode
• (d) electrolyte.

Correct Answer: (a)

Explanation: In electrolytic refining, the impure metal slab acts as the anode, while a thin sheet of pure metal acts as the cathode.

26. Nickel is purified by thermal decomposition of its:

• (a) hydride
• (b) chloride
• (c) azide
• (d) carbonyl.

Correct Answer: (d)

Explanation: Mond's process involves the thermal decomposition of nickel tetracarbonyl.

27. Auto-reduction process is used in the extraction of:

• (a) Cu and Hg
• (b) Zn and Hg
• (c) Cu and Al
• (d) Fe and Pb.

Correct Answer: (a)

Explanation: Metals with low reactivity, such as Copper (Cu) and Mercury (Hg), are extracted using autoreduction of their oxides/sulphides.

28. Froth floatation process is used for the concentration of:

• (a) oxide ores
• (b) sulphide ores
• (c) chloride ores
• (d) amalgams.

Correct Answer: (b)

Explanation: Froth flotation is the standard method for concentrating sulphide ores.

29. Malachite is an ore of:

• (a) iron
• (b) zinc
• (c) copper
• (d) mercury.

Correct Answer: (c)

Explanation: Malachite ($CuCO_{3} \cdot Cu(OH)_{2}$) is a basic carbonate ore of copper.

30. Heating mixture of $Cu_{2}O$ and $Cu_{2}S$ will give:

• (a) $CuO + CuS$
• (b) $Cu_{2}SO_{3}$
• (c) $Cu + SO_{2}$
• (d) $Cu + SO_{3}$

Correct Answer: (c)

Explanation: This reaction is a classic example of auto-reduction to yield metallic copper and sulphur dioxide gas.

31. Which one contains both iron and copper?

• (a) Cuprite
• (b) Chalcocite
• (c) Chalcopyrite
• (d) Malachite

Correct Answer: (c)

Explanation: Chalcopyrite ($CuFeS_{2}$) is a mixed sulphide containing both copper and iron.

32. Pb and Sn are extracted from their chief ores by:

• (a) carbon reduction and self reduction respectively
• (b) self reduction and carbon reduction respectively
• (c) electrolysis and self reduction respectively
• (d) self reduction and electrolysis respectively.

Correct Answer: (b)

Explanation: Lead chief ores can be self-reduced, whereas Tin ores require carbon reduction.

33. Which method of purification is represented by: $Ti_{(s)} + 2I_{2(g)} \xrightarrow{523 K} TiI_{4(g)} \xrightarrow{1700 K} Ti_{(s)} + 2I_{2(g)}$?

• (a) Mond process
• (b) Liquation
• (c) van Arkel
• (d) Zone refining

Correct Answer: (c)

Explanation: This sequence of reactions is the van Arkel method for refining Titanium or Zirconium.

34. Which of the following benefaction process is used for the mineral $Al_{2}O_{3} \cdot xH_{2}O$?

• (a) Froth-floatation
• (b) Leaching
• (c) Liquation
• (d) Magnetic separation

Correct Answer: (b)

Explanation: Leaching (such as the Baeyer's process) is used to purify bauxite ore.

35. In an Ellingham diagram with metal oxide curves X, Y, and Z (X at the bottom, Z at the top):

• (a) Y will reduce oxide Z.
• (b) Y will reduce oxide X.
• (c) Z will reduce oxide X.
• (d) Z will reduce oxide Y.

Correct Answer: (a)

Explanation: A metal lower in the Ellingham diagram (lower $\Delta G^{\circ}$) can reduce the oxide of a metal higher in the diagram.

36. Bauxite, an ore of aluminium contains impurities except:

• (a) $Fe_{2}O_{3}$
• (b) $SiO_{2}$
• (c) CuO
• (d) $TiO_{2}$

Correct Answer: (c)

Explanation: Standard impurities in bauxite include iron oxides, silica, and titanium oxide, but not copper oxide.

37. To obtain iron from their oxides, the method used is:

• (a) aluminothermic process
• (b) carbon monoxide reduction
• (c) electrolytic reduction
• (d) carbon reduction.

Correct Answer: (b)

Explanation: In industrial extraction (blast furnace), iron is primarily obtained through reduction by CO.

38. Which of the following is not correctly matched?

• (a) Complex formation and displacement: Ag and Au
• (b) Hydrometallurgy: Cu
• (c) Hall-Heroult process: Cd
• (d) Carbon reduction: Zn

Correct Answer: (c)

Explanation: The Hall-Heroult process is for Aluminum, not Cadmium.

39. Vapour phase refining is used for the purification of Ti because:

• (a) impurities more soluble in molten state
• (b) low melting Ti can flow on a surface
• (c) of formation of volatile $TiI_{4}$ which decomposes to extra pure Ti
• (d) none of these.

Correct Answer: (c)

Explanation: Vapour phase refining (van Arkel) works by creating a volatile intermediate ($TiI_{4}$) that is subsequently decomposed.

40. Sodium cyanide is added as a depressant in froth-floatation for ZnS/PbS ores because:

• (a) $Pb(CN)_{2}$ precipitates without effect on ZnS
• (b) ZnS forms soluble complex $[Zn(CN)_{4}]^{2-}$ while PbS forms froth
• (c) PbS forms soluble complex while ZnS forms froth
• (d) $Zn(CN)_{2}$ precipitates without effect on PbS.

Correct Answer: (b)

Explanation: NaCN acts as a depressant for ZnS by forming a soluble complex, allowing PbS to float preferentially.

41. Semiconductors of very high purity are obtained by:

• (a) liquation
• (b) vapour phase refining
• (c) zone refining
• (d) electrolysis.

Correct Answer: (c)

Explanation: Zone refining is used for obtaining ultra-pure semiconductors like Ge, Si, and B.

42. Which of the following reactions is an example of autoreduction?

• (a) $Fe_{3}O_{4} + 4CO \rightarrow 3Fe + 4CO_{2}$
• (b) $Cu_{2}O + C \rightarrow 2Cu + CO$
• (c) $Cu^{2+}_{(aq)} + Fe_{(s)} \rightarrow Cu_{(s)} + Fe^{2+}_{(aq)}$
• (d) $Cu_{2}O + \frac{1}{2}Cu_{2}S \rightarrow 3Cu + \frac{1}{2}SO_{2}$

Correct Answer: (d)

Explanation: In this reaction, no external reducing agent (like C or CO) is used; the sulphide and oxide of the metal react directly.

43. Copper matte is put in silica lined converter to:

• (a) remove $SiO_{2}$ as $FeSiO_{3}$ slag
• (b) oxidise $Cu_{2}S$ to $Cu_{2}O$
• (c) remove FeS, FeO and $Cu_{2}S/Cu_{2}O$ to metallic Cu
• (d) all of these.

Correct Answer: (d)

Explanation: The silica-lined converter performs multiple functions to eliminate impurities and obtain metallic copper from the matte.

44. Match column I (Process) with column II (Electrolyte): I. Down's cell, II. Dow sea water, III. Hall-Heroult, IV. Moissan.

• (a) I-Z, II-W, III-X, IV-Y
• (b) I-X, II-Y, III-Z, IV-W
• (c) I-W, II-Z, III-X, IV-Y
• (d) I-X, II-Z, III-W, IV-Y

Correct Answer: (a)

Explanation: Matches: Down's (fused NaCl/$CaCl_{2}$), Dow (fused $MgCl_{2}$), Hall-Heroult (fused Alumina/Cryolite), Moissan (fused $KHF_{2}$).

45. Select the true statement.

• (a) Below $710^{\circ}C$, C is better reducing agent than CO.
• (b) Below $710^{\circ}C$, CO is better reducing agent than C.
• (c) Below $710^{\circ}C$, CO is an oxidizing agent.
• (d) Below $710^{\circ}C$, $CO_{2}$ is reducing agent.

Correct Answer: (b)

Explanation: According to the Ellingham diagram, the CO curve is below the C curve at temperatures lower than $710^{\circ}C$, making it a more effective reducer.