MCQs on General Principles of Metallurgy – Class 12 Chemistry

Physical Chemistry – MCQ Titles (NCERT Based)
Course: CBSE Class 12 Chemistry – MCQs with Answers and Explanations

The following 50 NCERT-aligned MCQs are prepared strictly according to the CBSE Class 12 Chemistry chapter “General Principles of Metallurgy”. The questions are arranged section-wise to cover ores, concentration methods, extraction processes, thermodynamics, and refining, ensuring complete board exam readiness.

Section A: Basic Concepts of Metallurgy

1. Metallurgy is the process of:

A. Extraction of metals from ores
B. Purification of metals
C. Concentration of ores
D. All of the above

Correct Answer: D
Explanation: Metallurgy includes extraction, concentration, and refining of metals.

2. Naturally occurring compounds of metals are called:

A. Minerals
B. Ores
C. Gangue
D. Slag

Correct Answer: A
Explanation: Minerals are naturally occurring compounds; ores are minerals from which metal can be extracted profitably.

3. Ores differ from minerals because ores:

A. Are impure
B. Contain metals in free state
C. Allow economical extraction of metal
D. Are always oxides

Correct Answer: C
Explanation: Only those minerals from which metal extraction is economical are called ores.

4. Gangue refers to:

A. Metal impurities
B. Valuable components
C. Unwanted earthy impurities
D. Flux

Correct Answer: C
Explanation: Gangue consists of sand, clay, and rocky materials mixed with ore.

5. The first step in metallurgy is:

A. Roasting
B. Concentration of ore
C. Refining
D. Reduction

Correct Answer: B
Explanation: Concentration removes gangue from the ore.

Section B: Concentration of Ores

6. Which method is based on difference in wettability?

A. Hydraulic washing
B. Magnetic separation
C. Froth flotation
D. Leaching

Correct Answer: C
Explanation: Froth flotation exploits differences in wettability of ore and gangue.

7. Froth flotation is mainly used for:

A. Oxide ores
B. Sulphide ores
C. Carbonate ores
D. Halide ores

Correct Answer: B
Explanation: Sulphide ores are selectively wetted by oils.

8. Magnetic separation is used when:

A. Ore is magnetic
B. Gangue is magnetic
C. Either ore or gangue is magnetic
D. Both are non-magnetic

Correct Answer: C
Explanation: One component must be magnetic for separation.

9. Hydraulic washing is based on difference in:

A. Density
B. Magnetic property
C. Solubility
D. Reactivity

Correct Answer: A
Explanation: Heavier ore particles settle faster than lighter gangue.

10. Leaching involves:

A. Heating ore strongly
B. Dissolving ore in suitable reagent
C. Crushing ore
D. Roasting ore

Correct Answer: B
Explanation: Leaching selectively dissolves ore leaving impurities behind.

Section C: Conversion of Ore into Oxide

11. Roasting is carried out for:

A. Oxide ores
B. Sulphide ores
C. Carbonate ores
D. Native ores

Correct Answer: B
Explanation: Sulphide ores are converted into oxides by roasting.

12. Calcination is done in:

A. Excess air
B. Limited air
C. Absence of air
D. High pressure

Correct Answer: C
Explanation: Calcination involves heating in absence or limited air.

13. During calcination:

A. Oxides are converted to sulphides
B. Sulphides are oxidized
C. Carbonates are decomposed
D. Metals are reduced

Correct Answer: C
Explanation: Calcination removes CO₂ and water from ores.

14. Which gas is released during roasting?

A. CO₂
B. SO₂
C. H₂
D. O₂

Correct Answer: B
Explanation: Sulphur dioxide is released when sulphide ores are roasted.

15. Which process removes volatile impurities?

A. Refining
B. Calcination
C. Roasting
D. Both B and C

Correct Answer: D
Explanation: Both processes remove volatile impurities like CO₂ and SO₂.

Section D: Reduction of Metal Oxides

16. Which metal is extracted by carbon reduction?

A. Na
B. Mg
C. Fe
D. Al

Correct Answer: C
Explanation: Iron is moderately reactive and reduced by carbon.

17. Highly reactive metals are extracted by:

A. Chemical reduction
B. Electrolysis
C. Roasting
D. Smelting

Correct Answer: B
Explanation: Metals like Na, K, Al are extracted by electrolysis.

18. Which metal cannot be reduced by carbon?

A. Fe
B. Zn
C. Cu
D. Al

Correct Answer: D
Explanation: Aluminium is highly reactive and requires electrolysis.

19. Smelting involves:

A. Reduction with carbon
B. Heating with flux
C. Formation of slag
D. All of the above

Correct Answer: D
Explanation: Smelting reduces ore and removes impurities as slag.

20. Flux is added to:

A. Reduce metal oxide
B. Increase temperature
C. Remove gangue
D. Purify metal

Correct Answer: C
Explanation: Flux reacts with gangue to form slag.

Section E: Thermodynamic Principles of Metallurgy

21. Ellingham diagram shows variation of:

A. ΔG° with temperature
B. ΔH° with pressure
C. ΔS° with temperature
D. Energy with time

Correct Answer: A
Explanation: It plots Gibbs free energy change vs temperature.

22. A metal oxide lower in Ellingham diagram is:

A. Less stable
B. More stable
C. Easily reducible
D. Volatile

Correct Answer: B
Explanation: Lower position indicates greater stability.

23. Reduction of metal oxide is feasible when:

A. ΔG° is positive
B. ΔG° is zero
C. ΔG° is negative
D. Temperature is low

Correct Answer: C
Explanation: Negative Gibbs free energy indicates spontaneity.

24. Which reducing agent is strongest?

A. CO
B. H₂
C. C
D. Al

Correct Answer: D
Explanation: Aluminium is a very strong reducing agent.

25. Thermite reaction is used for:

A. Extraction of Na
B. Extraction of Fe
C. Welding of rails
D. Extraction of Al

Correct Answer: C
Explanation: Highly exothermic reaction used in welding.

Section F: Refining of Metals

26. Refining means:

A. Concentration of ore
B. Purification of metal
C. Reduction of oxide
D. Smelting

Correct Answer: B
Explanation: Refining removes impurities from crude metal.

27. Electrolytic refining is used for:

A. Na
B. Al
C. Cu
D. Mg

Correct Answer: C
Explanation: Copper is purified by electrolytic refining.

28. In electrolytic refining, pure metal is deposited at:

A. Anode
B. Cathode
C. Electrolyte
D. Slag

Correct Answer: B
Explanation: Metal ions gain electrons at cathode.

29. Impurities settle as:

A. Slag
B. Flux
C. Anode mud
D. Ore

Correct Answer: C
Explanation: Insoluble impurities collect as anode mud.

30. Zone refining is used for:

A. Low melting metals
B. Metals with high boiling point
C. Semiconductor metals
D. Alkali metals

Correct Answer: C
Explanation: Used for ultra-pure Si and Ge.

Section G: Special Extraction Processes

31. Gold is extracted by:

A. Froth flotation
B. Cyanide process
C. Magnetic separation
D. Smelting

Correct Answer: B
Explanation: Gold dissolves in cyanide solution.

32. Which metal is extracted by Hall–Héroult process?

A. Fe
B. Cu
C. Al
D. Zn

Correct Answer: C
Explanation: Aluminium is extracted electrolytically.

33. Cryolite is added during aluminium extraction to:

A. Increase purity
B. Decrease melting point
C. Act as catalyst
D. Remove impurities

Correct Answer: B
Explanation: Cryolite lowers melting point of alumina.

34. Bauxite is an ore of:

A. Iron
B. Aluminium
C. Zinc
D. Copper

Correct Answer: B
Explanation: Bauxite contains aluminium oxides.

35. Which metal occurs in native state?

A. Iron
B. Sodium
C. Gold
D. Aluminium

Correct Answer: C
Explanation: Gold is very unreactive.

Section H: Exam-Oriented MCQs

36. Slag is:

A. Metal oxide
B. Flux–gangue compound
C. Metal sulphide
D. Pure metal

Correct Answer: B
Explanation: Slag removes impurities.

37. Which ore is concentrated by leaching?

A. Bauxite
B. Zinc blende
C. Copper pyrites
D. Haematite

Correct Answer: A
Explanation: Bauxite is purified by Bayer’s process.

38. Which process emits SO₂ gas?

A. Calcination
B. Smelting
C. Roasting
D. Refining

Correct Answer: C
Explanation: Sulphide ores release SO₂ on roasting.

39. Which metal is extracted by self-reduction?

A. Zn
B. Cu
C. Al
D. Na

Correct Answer: B
Explanation: Copper sulphide partially reduces copper oxide.

40. Which ore is ZnS?

A. Calamine
B. Zincite
C. Zinc blende
D. Galena

Correct Answer: C
Explanation: ZnS is zinc blende.

41. Which is acidic flux?

A. CaO
B. SiO₂
C. MgO
D. Na₂CO₃

Correct Answer: B
Explanation: SiO₂ reacts with basic gangue.

42. Which refining method uses difference in melting point?

A. Distillation
B. Liquation
C. Electrolysis
D. Zone refining

Correct Answer: B
Explanation: Liquation separates low-melting metals.

43. Which metal is refined by distillation?

A. Cu
B. Zn
C. Fe
D. Al

Correct Answer: B
Explanation: Zinc has low boiling point.

44. Anode mud contains:

A. Pure metal
B. Gangue
C. Insoluble impurities
D. Flux

Correct Answer: C
Explanation: Precious metals settle as anode mud.

45. Which metal is least reactive?

A. Na
B. Al
C. Fe
D. Au

Correct Answer: D
Explanation: Gold lies lowest in reactivity series.

46. Extraction of aluminium is energy intensive because:

A. High melting point of alumina
B. Low conductivity
C. High reactivity of aluminium
D. All of these

Correct Answer: D
Explanation: Aluminium extraction requires high energy input.

47. Which reagent is used in cyanide process?

A. NaOH
B. NaCN
C. Na₂CO₃
D. NaCl

Correct Answer: B
Explanation: Sodium cyanide dissolves gold.

48. Which process converts ore into metal directly?

A. Concentration
B. Refining
C. Reduction
D. Roasting

Correct Answer: C
Explanation: Reduction gives metal from oxide.

49. Which metal can displace hydrogen from water?

A. Cu
B. Ag
C. Fe
D. Na

Correct Answer: D
Explanation: Sodium is highly reactive.

50. Metallurgy mainly aims to:

A. Study reactions
B. Obtain pure metals
C. Identify ores
D. Reduce pollution

Correct Answer: B
Explanation: Main goal is extraction and purification of metals.

✅ End of NCERT-Based MCQs on General Principles of Metallurgy – Class 12 Chemistry