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1. The primary function of a lubricant is to:
a) Increase friction
b) Reduce friction
c) Increase wear
d) Increase temperature
View Answer
b) Reduce friction
Explanation: Lubricants form a film between surfaces to minimize direct contact and frictional losses.
2. In hydrodynamic lubrication, load is supported by:
a) Chemical reaction film
b) Fluid pressure wedge
c) Solid lubricant layer
d) Asperity contact
View Answer
b) Fluid pressure wedge
Explanation: Convergent geometry and motion generate pressure to separate surfaces.
3. The Stribeck curve shows the relationship between:
a) Viscosity and temperature
b) Friction coefficient and Hersey number
c) Wear rate and load
d) Film thickness and speed
View Answer
b) Friction coefficient and Hersey number
Explanation: Hersey number = ηN/P; curve has three regimes: boundary, mixed, hydrodynamic.
4. ZDDP is used as:
a) Viscosity index improver
b) Anti-wear additive
c) Pour point depressant
d) Detergent
View Answer
b) Anti-wear additive
Explanation: Forms protective tribofilm (Zn/Fe phosphate) under boundary conditions.
5. The viscosity index (VI) of a lubricant is high when:
a) Viscosity increases sharply with temperature
b) Viscosity decreases sharply with temperature
c) Viscosity change is minimal with temperature
d) Viscosity is zero
View Answer
c) Viscosity change is minimal with temperature
Explanation: VI > 100 indicates good thermal stability (e.g., synthetics).
6. The flash point of a lubricant is the temperature at which:
a) It solidifies
b) Vapors ignite momentarily
c) It decomposes
d) It boils
View Answer
b) Vapors ignite momentarily
Explanation: Safety parameter; >200°C desirable for engine oils.
7. Pour point is important for lubricants used in:
a) High temperature
b) Cold weather
c) Vacuum
d) Acidic medium
View Answer
b) Cold weather
Explanation: Indicates lowest temperature for flow; < -20°C for winter oils.
8. Graphite is a good solid lubricant due to its:
a) High melting point
b) Layered structure with weak van der Waals forces
c) High hardness
d) Chemical reactivity
View Answer
b) Layered structure with weak van der Waals forces
Explanation: Layers slide easily; needs moisture for best performance.
9. In boundary lubrication, the film thickness is of the order of:
a) 1–100 μm
b) 0.1–1 μm
c) < 100 Å
d) > 1000 μm
View Answer
c) < 100 Å
Explanation: Monolayer; asperity contact occurs.
10. The lubricant used in space applications is preferably:
a) Mineral oil
b) Grease
c) MoS₂
d) Water
View Answer
c) MoS₂
Explanation: Works in vacuum; no volatility.
11. The additive used to improve viscosity index is:
a) ZDDP
b) Polymethacrylate
c) Calcium sulfonate
d) Benzotriazole
View Answer
b) Polymethacrylate
Explanation: Polymer coils expand at high temp → compensates viscosity drop.
12. Elastohydrodynamic lubrication is dominant in:
a) Journal bearings
b) Piston rings
c) Rolling contact bearings
d) Sliding pads
View Answer
c) Rolling contact bearings
Explanation: High pressure causes elastic deformation and viscosity increase.
13. The base oil in most engine lubricants is:
a) Vegetable oil
b) Mineral oil
c) Silicone oil
d) Animal fat
View Answer
b) Mineral oil
Explanation: ~90% of market; paraffinic/naphthenic fractions.
14. The four-ball test is used to determine:
a) Viscosity
b) Flash point
c) Wear and EP properties
d) Pour point
View Answer
c) Wear and EP properties
Explanation: ASTM D4172 (wear scar), D2783 (weld load).
15. The NLGI number indicates:
a) Viscosity of oil
b) Consistency of grease
c) VI of oil
d) Flash point
View Answer
b) Consistency of grease
Explanation: 000 (fluid) to 6 (hard); NLGI 2 most common.
16. The saponification value is high for:
a) Mineral oils
b) Synthetic oils
c) Vegetable oils
d) Silicones
View Answer
c) Vegetable oils
Explanation: Due to ester linkages; measures mg KOH/g oil.
17. The minimum friction in Stribeck curve occurs in:
a) Boundary regime
b) Hydrodynamic regime
c) Mixed regime
d) Dry friction
View Answer
c) Mixed regime
Explanation: Transition zone; partial fluid + boundary film.
18. Extreme pressure additives are essential in:
a) Journal bearings
b) Hypoid gears
c) Turbine oils
d) Hydraulic fluids
View Answer
b) Hypoid gears
Explanation: High sliding + load → need FeS/FeCl₂ sacrificial layer.
19. The cloud point of a lubricant indicates:
a) Wax crystallization
b) Flow cessation
c) Ignition
d) Boiling
View Answer
a) Wax crystallization
Explanation: First sign of turbidity; pour point is 3–5°C lower.
20. The best lubricant for high temperature (>300°C) is:
a) Mineral oil
b) PAO
c) Silicone oil
d) MoS₂
View Answer
d) MoS₂
Explanation: Solid lubricant; stable up to 800°C.
21. The detergent additive in engine oil:
a) Reduces viscosity
b) Neutralizes acids and cleans deposits
c) Increases pour point
d) Lowers flash point
View Answer
b) Neutralizes acids and cleans deposits
Explanation: Ca/Mg sulfonates keep engine clean.
22. The Hersey number is given by:
a) ηN/P
b) P/ηN
c) η/P
d) N/P
View Answer
a) ηN/P
Explanation: η = viscosity, N = speed, P = load.
23. Bio-lubricants are primarily derived from:
a) Petroleum
b) Vegetable oils
c) Coal tar
d) Animal fat only
View Answer
b) Vegetable oils
Explanation: Soy, canola, sunflower; biodegradable.
24. The RPVOT test measures:
a) Viscosity
b) Oxidation stability
c) Wear
d) Flash point
View Answer
b) Oxidation stability
Explanation: Rotating Pressure Vessel Oxidation Test (ASTM D2272).
25. The thickener in grease is usually:
a) Clay
b) Metal soap
c) Silica
d) All of these
View Answer
d) All of these
Explanation: Li, Ca, Na soaps; also polyurea, clay.
26. The API service category SN is for:
a) Diesel engines
b) Gasoline engines
c) Aviation
d) Marine
View Answer
b) Gasoline engines
Explanation: Latest for passenger cars (low phosphorus).
27. The main disadvantage of vegetable oil as lubricant is:
a) High cost
b) Poor oxidation stability
c) High viscosity
d) Low flash point
View Answer
b) Poor oxidation stability
Explanation: Unsaturated bonds → rancidity, sludge.
28. The Timken OK load test is for:
a) Viscosity
b) EP properties
c) Pour point
d) Cloud point
View Answer
b) EP properties
Explanation: Measures load-carrying capacity of gear oils.
29. Ionic liquids are emerging as lubricants due to:
a) Low cost
b) High thermal stability and low volatility
c) High friction
d) Poor film formation
View Answer
b) High thermal stability and low volatility
Explanation: Used in extreme conditions; green alternative.
30. The dropping point of grease indicates:
a) Flow start
b) Liquefaction temperature
c) Solidification
d) Flash point
View Answer
b) Liquefaction temperature
Explanation: Temperature at which grease becomes fluid (ASTM D566).
31. The best lubricant for food-grade applications is:
a) Mineral oil
b) White oil (NSF H1)
c) MoS₂
d) Graphite
View Answer
b) White oil (NSF H1)
Explanation: Incidental food contact approved.
32. The VI improver works by:
a) Reducing viscosity at low temp
b) Expanding polymer coils at high temp
c) Chemical reaction
d) Solid film formation
View Answer
b) Expanding polymer coils at high temp
Explanation: Compensates natural viscosity drop.
33. In EHL, viscosity increases due to:
a) Temperature rise
b) High pressure
c) Oxidation
d) Contamination
View Answer
b) High pressure
Explanation: Pressure-viscosity coefficient (α); up to 10⁶ times increase.
34. The main component of grease is:
a) Base oil (70–95%)
b) Thickener (5–30%)
c) Additive (1–5%)
d) Water
View Answer
a) Base oil (70–95%)
Explanation: Thickener gives structure; oil provides lubrication.
35. The anti-foam additive in lubricant is usually:
a) ZDDP
b) Silicone polymer
c) Calcium sulfonate
d) Graphite
View Answer
b) Silicone polymer
Explanation: Reduces surface tension of bubbles.
36. The oxidation of lubricant leads to:
a) Increased VI
b) Sludge and varnish formation
c) Decreased pour point
d) Increased flash point
View Answer
b) Sludge and varnish formation
Explanation: Antioxidants (amines, phenolics) prevent this.
37. The pour point depressant modifies:
a) Viscosity
b) Wax crystal structure
c) Flash point
d) Acidity
View Answer
b) Wax crystal structure
Explanation: Prevents large crystals → better flow at low temp.
38. The SAE grade 10W-40 indicates:
a) Single grade oil
b) Multigrade oil
c) Grease
d) Solid lubricant
View Answer
b) Multigrade oil
Explanation: 10W (winter flow), 40 (high temp viscosity).
39. The corrosion inhibitor in lubricant adsorbs on:
a) Oil surface
b) Metal surface
c) Water droplets
d) Air bubbles
View Answer
b) Metal surface
Explanation: Forms protective monolayer (e.g., benzotriazole on Cu).
40. The nano-additive in modern lubricants is:
a) Graphite
b) WS₂ inorganic fullerene
c) Clay
d) Silica
View Answer
b) WS₂ inorganic fullerene
Explanation: Rolling cage mechanism → ultra-low friction.
41. The base oil with highest oxidation stability is:
a) Paraffinic
b) Naphthenic
c) Aromatic
d) PAO
View Answer
d) PAO
Explanation: Polyalphaolefin; no unsaturation.
42. The GL-5 gear oil is recommended for:
a) Manual transmission
b) Hypoid gears
c) Worm gears
d) Chain drives
View Answer
b) Hypoid gears
Explanation: High EP additive level.
43. The emulsification number indicates:
a) Water separation tendency
b) Oil-water mixing
c) Foam stability
d) Acidity
View Answer
a) Water separation tendency
Explanation: Lower number → better demulsibility.
44. The best solid lubricant for vacuum is:
a) Graphite
b) MoS₂
c) PTFE
d) BN
View Answer
b) MoS₂
Explanation: Graphite needs adsorbed gases; MoS₂ works in dry vacuum.
45. The acid number of fresh oil should be:
a) > 1 mg KOH/g
b) < 0.1 mg KOH/g
c) 0.5–1 mg KOH/g
d) > 2 mg KOH/g
View Answer
b) < 0.1 mg KOH/g
Explanation: Indicates freshness; increase shows oxidation.
46. The synthetic oil with best low-temperature performance is:
a) Ester
b) PAO
c) Polyglycol
d) Silicone
View Answer
b) PAO
Explanation: Pour point < -60°C.
47. The dispersant in engine oil:
a) Cleans surfaces
b) Keeps soot in suspension
c) Reduces viscosity
d) Increases flash point
View Answer
b) Keeps soot in suspension
Explanation: Succinimide-based; prevents agglomeration.
48. The copper strip corrosion test is for:
a) Acidity
b) Sulfur content
c) Water content
d) Viscosity
View Answer
b) Sulfur content
Explanation: Active sulfur corrodes Cu (ASTM D130).
49. The lubricant for electric vehicle motors should have:
a) High viscosity
b) Low electrical conductivity
c) High phosphorus
d) High sulfur
View Answer
b) Low electrical conductivity
Explanation: Prevents short circuits; also low friction.
50. The future trend in lubrication is:
a) More mineral oil
b) Bio-lubricants and nano-additives
c) Higher sulfur
d) No additives
View Answer
b) Bio-lubricants and nano-additives
Explanation: Sustainability + performance (ILs, graphene, IF-WS₂).