RRB Technician Grade III 2024, 2025 PYQs

Concept: A colloid has particles of size about 1–1000 nm – between a true solution and a suspension.

1. It appears homogeneous but is actually a heterogeneous mixture.
2. Particles are too small to settle down when left undisturbed.
3. Particles scatter a beam of light – Tyndall effect.
4. So the statement 'colloid is a homogeneous mixture' is incorrect.

Yaad rakhein: Colloid: looks homogeneous, is heterogeneous, shows Tyndall effect, does not settle.

Answer: (A) Colloid is a homogeneous mixture.

Concept: Some plants reproduce vegetatively through their leaves.

1. In Bryophyllum, buds form in the notches along the leaf margin.
2. When the leaf falls on moist soil, these buds grow into new plants.
3. Grapes, rose and jasmine are usually propagated by stem cuttings or layering.

Yaad rakhein: Leaf buds in notches = Bryophyllum (patharchatta).

Answer: (B) Bryophyllum

Concept: Tiny air molecules scatter light of shorter wavelength much more than longer wavelength.

1. Blue light has a shorter wavelength than red, so it is scattered the most.
2. This scattered blue light reaches our eyes from all directions.
3. Hence the sky appears blue. Without atmosphere (e.g. in space) the sky looks dark.

Yaad rakhein: Blue sky, red sunrise/sunset, Tyndall effect – all due to scattering.

Answer: (A) Scattering of light

Concept: The fixed temperature at which a liquid turns into a solid on cooling is its freezing point.

1. For pure water, the freezing point is $0^{\circ }\text{C}$.
2. Melting point is for solid → liquid (on heating); for a pure substance both have the same value.
3. Boiling point is liquid → gas; condensation is gas → liquid.

Yaad rakhein: Cooling a liquid → freezing point; heating a solid → melting point.

Answer: (B) Freezing point

Concept: In myopia (near-sightedness) a person sees near objects clearly but not distant ones, because the image forms in front of the retina.

1. Cause: eye lens too converging (excessive curvature) or eyeball too long.
2. A concave (diverging) lens spreads the rays slightly before they enter the eye.
3. The image then forms exactly on the retina.

Trick: Myopia → Minus (concave) lens; Hypermetropia → convex (plus) lens.

Answer: (C) a concave lens of suitable power

Concept: A suspension is a heterogeneous mixture whose solid particles are large (above about 1000 nm).

1. Particles are big enough to be seen with the naked eye – statement true.
2. It is heterogeneous, not homogeneous.
3. Particles settle down when left undisturbed and can be separated by filtration.

Yaad rakhein: Suspension: visible particles, settles, filterable, scatters light (e.g. muddy water, chalk in water).

Answer: (A) The particles of a suspension can be seen by the naked eye.

Concept: Unicellular organisms reproduce by binary fission; the plane of division may be random or definite.

1. Leishmania (causes kala-azar) has a whip-like flagellum at one end.
2. Its binary fission occurs in a definite plane relative to the flagellum.
3. In Amoeba, fission can happen in any plane; Plasmodium shows multiple fission; yeast shows budding.

Yaad rakhein: Amoeba – any plane; Leishmania – definite plane; Plasmodium – multiple fission.

Answer: (D) Leishmania

Concept: In a parallel combination, every resistor is connected directly between the same two points P and Q.

1. So the potential difference across each resistor is the same → (A) correct.
2. Current divides: $I_1=\frac{V}{R_1}$, $I_2=\frac{V}{R_2}$.
3. If $R_1\ne R_2$, then $I_1\ne I_2$ → (B) incorrect. Total $I=I_1+I_2$.

Yaad rakhein: Series: same current; Parallel: same voltage.

Answer: (C) ‘A’ is correct and ‘B’ is incorrect.

Concept: Change of a liquid into vapour at any temperature below its boiling point is evaporation.

1. It is a surface phenomenon – only surface particles with enough energy escape.
2. Fusion = solid → liquid (melting); sublimation = solid → gas; deposition = gas → solid.
3. Evaporation increases with temperature, surface area and wind speed, and decreases with humidity.

Yaad rakhein: Evaporation causes cooling – e.g. sweating, earthen pot (matka) keeps water cool.

Answer: (C) evaporation

Concept: Newton's third law: to every action there is an equal and opposite reaction, acting on different bodies.

1. When the sailor jumps forward, he pushes the boat backward (action).
2. The boat pushes the sailor forward (reaction).
3. So the boat moves backward – a direct example of the third law (also momentum conservation).

Yaad rakhein: Recoil of gun, rocket launch, swimming, jumping from a boat – third law.

Answer: (A) Newton’s third law of motion

Concept: The Tyndall effect is the visible path of a light beam through a colloid, caused by scattering of light by its particles.

1. Colloidal particles are large enough to scatter light sideways.
2. The scattered light makes the beam's path visible.
3. Examples: sunlight beams through a dense forest canopy, light beam in a dusty room.

Yaad rakhein: True solution – no Tyndall effect; colloid & suspension – show it (scattering).

Answer: (A) Scattering of light

Concept: Refractive index $n=\frac{c}{v}$, so speed of light $v=\frac{c}{n}$ – lower $n$ means higher speed.

1. Values: water $1.33$, oil $1.46$, glycerine $1.5$, glass slab $1.65$.
2. Smallest $n=1.33$ (water).
3. So light travels fastest in water: $v=\frac{3\times {10}^8}{1.33}\approx 2.26\times {10}^8\text{ m/s}$.

Trick: Speed is inversely proportional to refractive index – pick the smallest $n$.

Answer: (C) water

Concept: Laws of reflection: (1) angle of incidence = angle of reflection; (2) incident ray, reflected ray and normal lie in the same plane.

1. These laws hold at every point of any reflecting surface.
2. For a spherical (curved) mirror, the normal at a point is along the radius through that point.
3. So the laws apply to plane as well as spherical surfaces.

Yaad rakhein: $\angle i=\angle r$ always – for plane, concave and convex mirrors alike.

Answer: (B) all types of reflecting surfaces including spherical surfaces

Concept: Atoms are extremely small; atomic radii are measured in nanometres ($1\text{ nm}={10}^{-9}\text{ m}$).

1. Radius of a hydrogen atom $\approx {10}^{-10}\text{ m}$ (about $0.1\text{ nm}$).
2. ${10}^{-8}\text{ m}$ is a large molecule/virus scale; ${10}^{-6}\text{ m}$ is bacterium scale.
3. ${10}^{-12}\text{ m}$ is too small for an atom (closer to nuclear sizes).

Yaad rakhein: NCERT table: atom ${10}^{-10}$ m, molecule of water ${10}^{-9}$ m, haemoglobin ${10}^{-8}$ m.

Answer: (C) ${10}^{-10}\text{ m}$

Concept: A human female has two ovaries containing thousands of immature eggs from birth.

1. From puberty, eggs start maturing.
2. Every month, one egg is released by one of the ovaries (ovulation).
3. The egg travels through the oviduct (fallopian tube) where fertilisation may occur.

Yaad rakhein: One egg per month, from alternate ovaries; no fertilisation → menstruation.

Answer: (C) One

Concept: Concentration depends on the amount of solute in a given amount of solvent.

1. Dilute: small amount of solute in a large amount of solvent.
2. Concentrated: large amount of solute in a small amount of solvent.
3. Any true solution, dilute or concentrated, is homogeneous.

Yaad rakhein: Adding more water makes a solution more dilute; adding more solute makes it more concentrated.

Answer: (B) It has a small amount of solute dissolved in a large amount of solvent.

Concept: In a non-dividing cell, the nucleus contains a tangled, thread-like mass called chromatin material.

1. Chromatin is made of DNA and proteins.
2. When the cell is about to divide, chromatin condenses into rod-shaped chromosomes.
3. DNA carries genetic information from parents to the next generation.

Yaad rakhein: Chromatin (non-dividing) → chromosomes (dividing); both = DNA + protein.

Answer: (B) DNA

Concept: A falling object speeds up because a force acts on it – the gravitational force of the Earth.

1. By Newton's second law, this force produces acceleration $g\approx 9.8{\text{ m/s}}^2$ towards the Earth.
2. Gravity is attractive, never repulsive.
3. Nuclear and electromagnetic forces do not cause objects to fall.

Yaad rakhein: Acceleration due to gravity $g=\frac{GM}{R^2}$ – same for all bodies (ignoring air).

Answer: (C) Earth’s gravitational force

Concept: To evaporate, water must absorb a large amount of heat – its latent heat of vaporisation (about $2.26\times {10}^6\text{ J/kg}$).

1. Water sprinkled on a hot roof takes this heat from the surface while evaporating.
2. The surface loses heat and cools down.
3. Because water's latent heat is large, the cooling effect is strong.

Yaad rakhein: Evaporation always causes cooling – sweat, wet cloth on the forehead, desert cooler.

Answer: (A) large latent heat of vaporisation of water helps to cool the hot surface

Concept: STDs can be bacterial or viral; identify the cause of each.

1. A. Gonorrhoea – bacterial (Neisseria gonorrhoeae).
2. B. AIDS – viral (HIV), so not bacterial.
3. C. Syphilis – bacterial (Treponema pallidum).
4. So the bacterial ones are A and C.

Yaad rakhein: Bacterial STDs: Gonorrhoea, Syphilis; Viral STDs: AIDS (HIV), warts (HPV).

Answer: (C) Both A and C