Multiple Choice Questions (MCQs) and Explanations

Here are 40 MCQs based on the “General Principles and Processes of Isolation of Elements (Metallurgy)” notes, with detailed explanations.

Question 1: Which of the following is an ore of aluminium?

(A) Magnetite (Fe3​O4​)

(B) Bauxite (Al2​O3​⋅2H2​O)

(C) Zinc blend (ZnS)

(D) Haematite (Fe2​O3​)

Correct Answer: (B)

Reasoning: Bauxite is the principal ore of aluminium. Magnetite and Haematite are iron ores, and zinc blend is a zinc ore.

Question 2: The process of removing unwanted earthy and rocky materials from the ore is called:

(A) Calcination

(B) Roasting

(C) Smelting

(D) Concentration (Beneficiation)

Correct Answer: (D)

Reasoning: Concentration, beneficiation, or ore dressing are terms used for the initial step of removing gangue from the ore. Calcination and roasting are heat treatments, and smelting is reduction.

Question 3: Froth floatation process is generally used for the concentration of:

(A) Oxide ores

(B) Carbonate ores

(C) Sulphide ores

(D) Silicate ores

Correct Answer: (C)

Reasoning: The froth floatation process selectively separates sulphide ores from gangue based on their preferential wetting by oil.

Question 4: What is the purpose of adding flux during smelting?

(A) To increase the melting point of the ore.

(B) To remove fusible impurities.

(C) To remove non-fusible gangue as fusible slag.

(D) To reduce the metal oxide.

Correct Answer: (C)

Reasoning: Flux is added to combine with the non-fusible gangue present in the ore, forming an easily fusible product called slag, which can be separated.

Question 5: Which of the following metals is purified by the Mond’s process?

(A) Zinc

(B) Copper

(C) Nickel

(D) Aluminium

Correct Answer: (C)

Reasoning: Mond’s process is a vapour phase refining method specifically used for the purification of nickel, involving the formation and decomposition of volatile nickel tetracarbonyl.

Question 6: In the electrolytic refining of copper, the impure copper is made the:

(A) Anode

(B) Cathode

(C) Electrolyte

(D) Salt bridge

Correct Answer: (A)

Reasoning: In electrolytic refining, the impure metal is made the anode, where it undergoes oxidation and dissolves into ions. Pure metal ions from the electrolyte then deposit on the cathode.

Question 7: The main reaction occurring during roasting of a sulphide ore is:

(A) Conversion to carbonate.

(B) Conversion to oxide.

(C) Conversion to sulphide.

(D) Reduction to metal.

Correct Answer: (B)

Reasoning: Roasting is the process of heating a sulphide ore in excess air to convert it into its corresponding metal oxide and liberate sulphur dioxide gas.

Question 8: Which of the following processes is used for the extraction of aluminium from purified alumina?

(A) Smelting with carbon

(B) Electrolytic reduction (Hall-Héroult process)

(C) Thermite process

(D) Self-reduction

Correct Answer: (B)

Reasoning: Aluminium is a highly reactive metal, and its oxide (Al2​O3​) is very stable. Therefore, it is extracted by electrolytic reduction (Hall-Héroult process) of molten alumina mixed with cryolite and fluorspar.

Question 9: Zone refining is used for the purification of:

(A) Low boiling metals like Zn.

(B) Metals with low melting points like Sn.

(C) Ultra-pure metals for semiconductors like Si and Ge.

(D) Impure metals that form volatile compounds.

Correct Answer: (C)

Reasoning: Zone refining is based on the principle that impurities are more soluble in the molten state. It is used to obtain metals of very high purity, especially for semiconductors like Silicon (Si) and Germanium (Ge).

Question 10: An acidic flux is used to remove which type of gangue?

(A) Acidic gangue

(B) Basic gangue

(C) Neutral gangue

(D) Sulphide gangue

Correct Answer: (B)

Reasoning: Acidic flux (e.g., SiO2​) reacts with basic gangue (e.g., FeO, CaO) to form fusible slag.

Question 11: The cyanide process (leaching with NaCN) is used for the extraction of:

(A) Iron

(B) Copper

(C) Zinc

(D) Gold and Silver

Correct Answer: (D)

Reasoning: Gold and silver are extracted by leaching their finely powdered ores with a dilute solution of sodium or potassium cyanide in the presence of air, forming soluble cyano complexes.

Question 12: Which process involves heating the ore in the absence of air below its melting point?

(A) Roasting

(B) Smelting

(C) Calcination

(D) Liquation

Correct Answer: (C)

Reasoning: Calcination is the process of heating the ore in a limited supply of air or in the absence of air to remove volatile impurities and convert carbonates/hydroxides to oxides. Roasting involves heating in excess air.

Question 13: The slag formed during the extraction of iron in a blast furnace is:

(A) FeSiO3​

(B) CaSiO3​

(C) Al2​O3​

(D) SiO2​

Correct Answer: (B)

Reasoning: In the blast furnace, the gangue is silica (SiO2​), and the flux is limestone (CaCO3​, which decomposes to CaO). CaO reacts with SiO2​ to form calcium silicate (CaSiO3​) slag.

Question 14: Which of the following reduction methods is used for highly reactive metals like sodium and potassium?

(A) Carbon reduction

(B) Self-reduction

(C) Electrolytic reduction

(D) Aluminothermy

Correct Answer: (C)

Reasoning: Highly reactive metals have very stable oxides (and halides). Therefore, they are extracted by the electrolytic reduction of their molten salts (e.g., molten NaCl for Na, molten Al2​O3​ for Al).

Question 15: Van Arkel method is used for the purification of:

(A) Nickel

(B) Copper

(C) Zirconium and Titanium

(D) Zinc

Correct Answer: (C)

Reasoning: The van Arkel method is a vapour phase refining technique used to obtain ultra-pure Zirconium (Zr) and Titanium (Ti) by converting them into volatile iodides and then decomposing them.

Question 16: In the Hall-Héroult process, cryolite (Na3​AlF6​) is added to alumina to:

(A) Act as a flux to remove impurities.

(B) Lower the melting point of alumina and increase its conductivity.

(C) Act as a reducing agent.

(D) Prevent the oxidation of aluminium.

Correct Answer: (B)

Reasoning: Alumina has a very high melting point. Cryolite and fluorspar are added to lower the melting point of the mixture significantly and to increase its electrical conductivity, making the electrolysis feasible.

Question 17: Which diagram is used to predict the feasibility of reduction of an oxide by another element?

(A) Pourbaix diagram

(B) Frost diagram

(C) Ellingham diagram

(D) Latimer diagram

Correct Answer: (C)

Reasoning: The Ellingham diagram plots ΔG∘ vs T for the formation of metal oxides and is extensively used to predict the thermodynamic feasibility of reducing metal oxides.

Question 18: The process of hydraulic washing is based on the principle of:

(A) Magnetic properties.

(B) Difference in densities.

(C) Wetting properties.

(D) Chemical reactivity.

Correct Answer: (B)

Reasoning: Hydraulic washing (gravity separation) utilizes the difference in specific gravities (densities) between the heavier ore particles and the lighter gangue particles.

Question 19: What is anode mud in electrolytic refining?

(A) Impurities that settle at the bottom of the anode.

(B) Pure metal deposited at the anode.

(C) The electrolyte solution.

(D) Slag formed during the process.

Correct Answer: (A)

Reasoning: During electrolytic refining, more noble (less reactive) metal impurities (like gold, silver, platinum) present in the impure anode do not get oxidized and fall off, collecting as “anode mud” at the bottom of the anode.

Question 20: The self-reduction process is used for which type of ores?

(A) Highly stable oxides

(B) Carbonate ores

(C) Partially roasted sulphide ores

(D) Halide ores

Correct Answer: (C)

Reasoning: Self-reduction (or auto-reduction) occurs with certain sulphide ores (e.g., PbS, Cu2​S, HgS) where a part of the ore is roasted to form oxide, and this oxide then reacts with the remaining sulphide to produce the metal without an external reducing agent.

Question 21: What is the chemical formula of cryolite?

(A) CaF2​

(B) AlF3​

(C) Na3​AlF6​

(D) Al2​O3​

Correct Answer: (C)

Reasoning: Cryolite is sodium hexafluoroaluminate (Na3​AlF6​), an essential component in the Hall-Héroult process.

Question 22: Which refining method is used for metals having low boiling points?

(A) Liquation

(B) Zone refining

(C) Distillation

(D) Electrolytic refining

Correct Answer: (C)

Reasoning: Distillation is suitable for volatile metals like Zinc, Cadmium, and Mercury, which have low boiling points.

Question 23: In the context of Ellingham diagrams, a metal can reduce the oxide of another metal if its ΔG∘ vs T line lies:

(A) Above the oxide to be reduced.

(B) Below the oxide to be reduced.

(C) Intersects the oxide to be reduced at 0 K.

(D) Is parallel to the oxide to be reduced.

Correct Answer: (B)

Reasoning: For a reduction to be thermodynamically feasible, the overall ΔG∘ for the coupled reaction (oxidation of reducing agent + reduction of metal oxide) must be negative. This occurs when the line for the formation of the reducing agent’s oxide lies below the line for the metal oxide to be reduced on the Ellingham diagram.

Question 24: Leaching of gold involves treatment with:

(A) H2​SO4​

(B) NaOH solution

(C) Dilute NaCN solution in presence of air

(D) Concentrated HCl

Correct Answer: (C)

Reasoning: Gold is leached using a dilute sodium cyanide solution in the presence of air to form a soluble dicyanoaurate(I) complex.

Question 25: Which of the following is not a step in the concentration of ores?

(A) Hydraulic washing

(B) Magnetic separation

(C) Roasting

(D) Froth floatation

Correct Answer: (C)

Reasoning: Roasting is a process of converting sulphide ores to oxides (thermal treatment), which occurs after concentration, not a concentration method itself.

Question 26: The gas liberated during the roasting of sulphide ores is used for the manufacture of:

(A) Chlorine

(B) Sulphuric acid

(C) Ammonia

(D) Nitric acid

Correct Answer: (B)

Reasoning: Sulphide ores typically produce sulphur dioxide (SO2​) gas upon roasting, which is a key raw material for the production of sulphuric acid (H2​SO4​) via the contact process.

Question 27: Which process is based on the principle that impurities are more soluble in the molten state than in the solid state of the metal?

(A) Distillation

(B) Liquation

(C) Zone refining

(D) Electrolytic refining

Correct Answer: (C)

Reasoning: Zone refining explicitly uses this principle to achieve ultra-high purity in metals.

Question 28: What is the chemical formula of rust?

(A) Fe2​O3​

(B) Fe2​O3​⋅xH2​O

(C) Fe(OH)2​

(D) FeO

Correct Answer: (B)

Reasoning: Rust is hydrated ferric oxide, with the chemical formula Fe2​O3​⋅xH2​O, where ‘x’ represents a variable number of water molecules.

Question 29: In the electrolytic reduction of alumina, which electrodes are consumed?

(A) Cathode (carbon lining)

(B) Anode (graphite rods)

(C) Both anode and cathode

(D) Neither

Correct Answer: (B)

Reasoning: The oxygen evolved at the anode reacts with the carbon anodes (graphite rods), consuming them and forming CO and CO2​ gases.

Question 30: A basic flux is used to remove:

(A) Basic impurities

(B) Acidic impurities

(C) Neutral impurities

(D) Magnetic impurities

Correct Answer: (B)

Reasoning: Basic flux (e.g., CaO) reacts with acidic gangue (e.g., SiO2​) to form fusible slag.

Question 31: What is the oxidation state of aluminium in cryolite (Na3​AlF6​)?

(A) +1

(B) +2

(C) +3

(D) 0

Correct Answer: (C)

Reasoning: In Na3​AlF6​, Na is +1 (3×+1=+3), and F is -1 (6×−1=−6). To balance the charge in the complex ion [AlF6​]3−, Al must be +3 (+3−6=−3).

Question 32: The process of connecting a metal to be protected from corrosion to a more active metal is called:

(A) Painting

(B) Alloying

(C) Sacrificial protection

(D) Electroplating

Correct Answer: (C)

Reasoning: Sacrificial protection (or cathodic protection) involves connecting a more electropositive (active) metal to the metal to be protected. The more active metal corrodes preferentially, thus saving the desired metal.

Question 33: Which refining method involves the formation of a volatile metal compound that is then decomposed to pure metal?

(A) Liquation

(B) Distillation

(C) Vapour phase refining

(D) Zone refining

Correct Answer: (C)

Reasoning: Vapour phase refining (e.g., Mond’s process, van Arkel method) relies on the formation of a volatile compound of the metal, followed by its decomposition to yield the pure metal.

Question 34: The Kroll process is specifically used for the extraction of:

(A) Zinc

(B) Iron

(C) Titanium

(D) Gold

Correct Answer: (C)

Reasoning: The Kroll process is a specific industrial method for producing titanium metal by reducing titanium tetrachloride (TiCl4​) with magnesium.

Question 35: What is the role of air (oxygen) in the leaching of gold by the cyanide process?

(A) To provide an acidic medium.

(B) To act as a solvent.

(C) To oxidize the metal for complex formation.

(D) To reduce the complex back to metal.

Correct Answer: (C)

Reasoning: Oxygen acts as an oxidizing agent in the cyanide leaching process, oxidizing the elemental gold (or silver) to its ionic form (Au+/Ag+) so it can form the soluble cyano complex.

Question 36: Which of the following is an example of a basic flux?

(A) SiO2​

(B) P4​O10​

(C) CaO

(D) SO2​

Correct Answer: (C)

Reasoning: Calcium oxide (CaO) is a basic oxide and is used as a basic flux to remove acidic impurities like SiO2​.

Question 37: In the blast furnace, at lower temperatures (500-800 K), iron oxide is primarily reduced by:

(A) Coke (carbon)

(B) Limestone (CaCO3​)

(C) Carbon monoxide (CO)

(D) Hydrogen (H2​)

Correct Answer: (C)

Reasoning: At lower temperatures in the blast furnace, carbon monoxide (CO) is the main reducing agent for iron oxides. At higher temperatures, carbon itself acts as the reducing agent.

Question 38: Which type of ore concentration method involves the use of depressants?

(A) Hydraulic washing

(B) Magnetic separation

(C) Froth floatation

(D) Leaching

Correct Answer: (C)

Reasoning: Depressants (like NaCN) are used in the froth floatation process to selectively prevent certain sulphide ores from forming froth, allowing the separation of a mixture of sulphide ores.

Question 39: The term “gangue” refers to:

(A) The pure metal.

(B) The valuable mineral in the ore.

(C) Unwanted rocky or earthy impurities in the ore.

(D) The fusible product formed during smelting.

Correct Answer: (C)

Reasoning: Gangue (or matrix) is the unwanted material associated with the ore.

Question 40: Which refining method is based on the principle of differential adsorption on an adsorbent?

(A) Electrolytic refining

(B) Zone refining

(C) Vapour phase refining

(D) Chromatographic methods

Correct Answer: (D)

Reasoning: Chromatographic methods (like column chromatography) separate components based on their different affinities for (adsorption onto) a stationary phase. They are used for highly pure separations, especially when impurities are in trace amounts.