Q60. When water is poured slowly from a jug and clings to its side, which property chiefly accounts for this behaviour?
[UPSC NDA-II – 2026]
(A) Surface tension
(B) Low vapour pressure
(C) Negligible compressibility
(D) Low viscosity
Answer: (A) Surface tension
Explanation: Surface tension, together with adhesion to the jug surface, makes water follow the spout or edge rather than separate immediately. Cohesive attraction helps maintain the thin liquid sheet. The phenomenon is familiar when water trickles down a vessel while pouring.
Q59. Which physical property is generally characteristic of metals?
[RRB Group D – August 2026]
(A) They conduct heat poorly
(B) They have metallic lustre and conduct electricity well
(C) They are invariably brittle
(D) Every metal is solid at room temperature
Answer: (B) They have metallic lustre and conduct electricity well
Explanation: Most metals reflect light strongly and contain mobile electrons, which help carry electrical current. They also tend to conduct heat efficiently. Mercury is liquid at ordinary room temperature, so a claim that every metal is solid would be incorrect.
Q58. Of sulphur, diamond and bromine, which property would be least likely to be common to all three samples?
[RRB Group D – August 2026]
(A) Poor thermal conduction
(B) High electrical conductivity
(C) Brittleness
(D) Dull appearance
Answer: (B) High electrical conductivity
Explanation: These are non-metallic substances, and high electrical conductivity is not their shared characteristic. Diamond conducts heat exceptionally well but is a poor electrical conductor; bromine is liquid at room temperature. Generalisations about other properties should therefore be treated cautiously.
Q57. How do non-metals generally behave in terms of electrical conduction in their pure forms?
[RRB Group D – August 2026]
(A) They are excellent conductors
(B) They usually do not conduct electricity
(C) They conduct as efficiently as metals
(D) They always have metallic conductivity
Answer: (B) They usually do not conduct electricity
Explanation: Most non-metals lack freely moving charge carriers, making them poor electrical conductors. Graphite is an important exception because its delocalised electrons can carry current. The examination tests the general trend, not an exception-free rule for every non-metal.
Q56. Consider ocean currents:
(1) water-density differences drive important currents;
(2) seawater density depends on temperature, salinity and pressure;
(3) currents always flow from denser to less dense water.
Which statements are correct?
[UPSC CDS-I – 2026]
(A) 1 and 2 only
(B) 1 only
(C) 1, 2 and 3
(D) 2 and 3 only
Answer: (A) 1 and 2 only
Explanation: Differences in temperature and salinity produce density contrasts that drive thermohaline circulation. Pressure also affects seawater density. The proposed universal flow direction is oversimplified: currents depend on pressure gradients, wind, gravity, Earth rotation and vertical density structure.
Q55. For a floating object in stable equilibrium, where must its centre of gravity lie?
[UPSC NDA-I – 2026]
(A) Above its centre of buoyancy
(B) Below its centre of buoyancy in every case
(C) Exactly at its centre of buoyancy
(D) Below its metacentre
Answer: (D) Below its metacentre
Explanation: A freely floating body is stable against small tilting when its metacentre lies above its centre of gravity. That position produces a restoring moment. The centre of gravity need not lie below the centre of buoyancy for stability.
Q54. What term refers to the gaps or spaces between constituent particles in a solid?
[RRB Group D – January 2026]
(A) Inter-particle space
(B) Density
(C) Rigidity
(D) Compressibility
Answer: (A) Inter-particle space
Explanation: Inter-particle spaces are the microscopic gaps between atoms, ions or molecules. They are usually comparatively small in solids, where particles occupy closely packed positions. Rigidity describes resistance to deformation, whereas density expresses the amount of mass per unit volume.
Q53. A hydrometer measures the density of a liquid. Which physical principle explains its operation?
[RRB Group D – December 2025]
(A) Pascal’s law
(B) Universal gravitation alone
(C) Archimedes’ principle
(D) Newton’s first law
Answer: (C) Archimedes’ principle
Explanation: A hydrometer floats at a depth determined by the liquid density. Archimedes’ principle states that buoyant force equals the weight of fluid displaced. The instrument sinks further in less-dense liquids and floats higher when liquid density increases.
Q52. Which is the SI unit used to express the density of matter?
[RRB Group D – December 2025]
(A) Kilogram per cubic metre
(B) Kilogram per square metre
(C) Kilogram per metre
(D) Gram per metre
Answer: (A) Kilogram per cubic metre
Explanation: Density is mass divided by volume. In the SI system, mass is measured in kilograms and volume in cubic metres, giving kg/m³. The unit describes the mass contained in each unit volume of a substance at specified conditions.
Q51. Which property normally describes solid non-metals?
[RRB Group D – December 2025]
(A) High density and high melting point without exception
(B) Malleability and ductility
(C) Brittleness
(D) Excellent electrical conductivity
Answer: (C) Brittleness
Explanation: Many solid non-metals fracture when force is applied instead of being rolled into sheets or drawn into wires. They are consequently described as brittle. Graphite and diamond illustrate how non-metals can nevertheless have markedly different physical properties.