RRB Technician Grade III 2024, 2025 PYQs

Concept: Solid $\mathrm{C}{\mathrm{O}}_2$ (dry ice) is stored under high pressure. When pressure decreases to 1 atmosphere, it changes directly into gas without becoming liquid (sublimation).

1. High pressure keeps $\mathrm{C}{\mathrm{O}}_2$ solid.
2. Lowering pressure to 1 atm → direct solid → gas.
3. Hence called 'dry ice'.

Yaad rakhein: Dry ice → 1 atmosphere → sublimation.

Answer: (A) 1 atmosphere

Concept: Human excretory system: a pair of kidneys, a pair of ureters, one urinary bladder and one urethra.

1. Kidney – a pair ✔
2. Ureter – a pair ✔
3. Urinary bladder – unpaired ✔
4. Urethra – single, not a pair ✘

Trick: Count '2-2-1-1': kidneys 2, ureters 2, bladder 1, urethra 1.

Answer: (A) Urethra – a pair

Concept: Electric power $P=V\times I$.

1. $V=200\text{V},I=0.1\text{A}$
2. $P=200\times 0.1=20\text{W}$

Trick: Multiplying by $0.1$ just shifts the decimal one place: $200\to 20$.

Answer: (B) 20 W

Concept: Puberty brings specific changes caused by sex hormones, such as new hair growth in armpits, thinner hair on arms and legs, and breast development in girls.

1. Thick hair in armpits, thinner hair on legs/arms, increase in breast size → puberty-specific.
2. Increase in height happens throughout childhood as well.
3. So height increase is not specific to teenage.

Yaad rakhein: Puberty-specific = hormone-driven secondary sexual characters; general growth is not.

Answer: (B) Increase in height

Concept: Metals react with dilute acids to form a salt and hydrogen gas.

1. $\text{Metal}+\text{dil. HCl}\to \text{Metal chloride}+{\mathrm{H}}_2$
2. e.g. $\mathrm{Z}\mathrm{n}+2\mathrm{H}\mathrm{C}\mathrm{l}\to \mathrm{Z}\mathrm{n}\mathrm{C}{\mathrm{l}}_2+{\mathrm{H}}_2$
3. Test: gas burns with a 'pop' sound.

Yaad rakhein: Pop sound with burning splinter = hydrogen.

Answer: (D) Hydrogen

Concept: Force $F=ma$, where acceleration $a=\frac{v-u}{t}$.

1. $a=\frac{10-6}{2}=2{\text{m/s}}^2$
2. $F=10\times 2=20\text{N}$

Trick: $F=\frac{m(v-u)}{t}=\frac{10\times 4}{2}=20$ — change in momentum per second.

Answer: (C) 20 N

Concept: Unsaturated hydrocarbons contain at least one carbon–carbon double or triple bond.

1. Alkenes have $\mathrm{C}=\mathrm{C}$; alkynes have $\mathrm{C}\equiv \mathrm{C}$ → unsaturated.
2. Alkanes (methane, ethane, butane) have only single bonds → saturated.
3. Cyclopentane and cyclohexane also have only single bonds → saturated.

Yaad rakhein: '-ane' = saturated; '-ene' and '-yne' = unsaturated.

Answer: (C) Alkenes and alkynes are unsaturated hydrocarbons.

Concept: Oestrogen, secreted by the ovaries, controls development of female sex organs, secondary sexual characters and regulates the menstrual cycle.

1. Adrenaline – emergency (fight or flight) hormone.
2. Thyroxin – regulates metabolism.
3. Testosterone – male hormone from testes.

Yaad rakhein: Ovary → oestrogen (female); testis → testosterone (male).

Answer: (C) Oestrogen

Concept: Nitric acid is a strong oxidising agent: it oxidises the ${\mathrm{H}}_2$ formed to water, so usually no hydrogen is evolved. Only Mg and Mn give ${\mathrm{H}}_2$ with very dilute $\mathrm{H}\mathrm{N}{\mathrm{O}}_3$.

1. $\mathrm{M}\mathrm{g}+2\mathrm{H}\mathrm{N}{\mathrm{O}}_3\to \mathrm{M}\mathrm{g}(\mathrm{N}{\mathrm{O}}_3{)}_2+{\mathrm{H}}_2$
2. $\mathrm{M}\mathrm{n}+2\mathrm{H}\mathrm{N}{\mathrm{O}}_3\to \mathrm{M}\mathrm{n}(\mathrm{N}{\mathrm{O}}_3{)}_2+{\mathrm{H}}_2$
3. Copper is below hydrogen in reactivity — gives no ${\mathrm{H}}_2$ with dilute acids.

Trick: 'M-M' rule: Magnesium and Manganese with very dilute nitric acid.

Answer: (A) Magnesium (Mg) and manganese (Mn)

Concept: The colour of scattered light depends on the size of the scattering particles.

1. Very fine particles scatter mainly blue light (shorter wavelength).
2. Larger particles scatter longer wavelengths too.
3. Very large particles scatter all colours → light looks white (e.g. clouds).

Yaad rakhein: Blue sky = tiny air molecules; white clouds = big water droplets.

Answer: (C) The size of the scattering particles.

Concept: Sun rays (parallel) converge at the principal focus, so $f=30\text{cm}$. For a concave mirror, an object at the centre of curvature $C$ ($2f$) gives a real, inverted image of the same size at $C$.

1. $f=30\text{cm}$
2. $R=2f=60\text{cm}$
3. Object at $C$ → image at $C$, same size.

Yaad rakhein: Same size image in a concave mirror only when object is at $C$ ($u=2f$).

Answer: (A) 60 cm in front of the mirror

Concept: An electric bulb converts electrical energy mainly into light energy (along with some heat).

1. Current heats the tungsten filament.
2. The white-hot filament glows and emits light.
3. Useful output = light energy.

Yaad rakhein: Bulb → light; fan → mechanical (kinetic); heater → heat.

Answer: (D) Light

Concept: Saliva contains the enzyme salivary amylase, which breaks down starch into simple sugar (maltose) in the mouth.

1. Pepsin – stomach, digests proteins.
2. Trypsin – pancreatic juice, digests proteins.
3. Starch digestion begins in the mouth by amylase.

Yaad rakhein: Salivary amylase is also called ptyalin.

Answer: (A) Amylase enzymes

Concept: Tropism is directional growth movement of a plant part in response to a stimulus.

1. Phototropism → light (not water) ✘
2. Hydrotropism → water ✔
3. Chemotropism → chemicals ✔
4. Geotropism → gravity ✔

Trick: Photo = light, hydro = water, geo = earth, chemo = chemical.

Answer: (A) Phototropism – movement towards water

Concept: Parenchyma has living, loosely packed, unspecialised thin-walled cells; aerenchyma (with air cavities) helps aquatic plants float.

1. Flexibility for bending of tendrils and stems of climbers is given by collenchyma, not parenchyma.
2. Options B, C and D correctly describe parenchyma.
3. So option A is incorrect.

Yaad rakhein: Collenchyma → flexibility; sclerenchyma → hardness; parenchyma → storage and support.

Answer: (A) It allows the bending of various parts of a plant like tendrils and stems of climbers without breaking.

Concept: 'Dropped' means the object is released from rest, so its initial velocity $u=0$.

1. Dropped → $u=0$
2. Only the final speed depends on height: $v=\sqrt{2gh}$.
3. Height 50 m is extra data here.

Trick: Dropped / released / starts from rest → $u=0$; thrown → $u\ne 0$.

Answer: (B) 0

Concept: A convex mirror diverges a parallel beam; its focus lies behind the mirror, so by sign convention its focal length is positive.

1. Diverging mirror → convex ✔ (i)
2. Focus behind mirror → $f>0$ ✔ (ii)
3. Image is always virtual, erect, diminished → cannot be obtained on a screen ✘ (iii)

Yaad rakhein: Convex mirror: $f$ positive, image virtual; concave mirror: $f$ negative.

Answer: (C) Both (i) and (ii)

Concept: Meristematic cells are actively dividing cells with dense cytoplasm, thin cellulose walls and prominent nuclei, but they lack vacuoles.

1. Cytoplasm – dense ✔ present
2. Cell wall – thin ✔ present
3. Nucleus – prominent ✔ present
4. Vacuoles – absent ✘

Yaad rakhein: Vacuoles store food/waste; dividing cells don't need them.

Answer: (C) Vacuoles

Concept: A suspension is a heterogeneous mixture with particles large enough to be seen by naked eye.

1. (i) Heterogeneous mixture ✔
2. (ii) Particles scatter light, path is visible ✔
3. (iii) Particles settle down on standing — unstable ✔

Yaad rakhein: Suspension: visible particles, Tyndall effect, settles, separable by filtration.

Answer: (A) i, ii and iii

Concept: In refraction, light bends at the boundary of two media, so the angle of refraction is generally not equal to the angle of incidence ($\frac{\sin i}{\sin r}=\text{constant}$).

1. Speed of light differs for different colours in a medium ✔ (causes dispersion)
2. Incident ray, refracted ray and normal lie in one plane ✔
3. Speed differs in different media ✔
4. Equal angles is the law of reflection, not refraction ✘

Yaad rakhein: $\angle i=\angle r$ → reflection; Snell's law → refraction.

Answer: (C) The angle of incidence and refraction are equal.