RRB Technician Grade III 2024, 2025 PYQs

Concept: Bleaching powder is made by passing chlorine gas over dry slaked lime.

1. $\mathrm{C}\mathrm{a}(\mathrm{O}\mathrm{H}{)}_2+\mathrm{C}{\mathrm{l}}_2\to \mathrm{C}\mathrm{a}\mathrm{O}\mathrm{C}{\mathrm{l}}_2+{\mathrm{H}}_2\mathrm{O}$.
2. The chlorine comes from the chlor-alkali process.
3. $\mathrm{C}\mathrm{a}\mathrm{O}\mathrm{C}{\mathrm{l}}_2$ is used for bleaching and disinfecting drinking water.

Yaad rakhein: Bleaching powder = dry slaked lime + chlorine.

Answer: (B) Chlorine gas

Concept: $W=Fs\cos \theta$, where $\theta$ is the angle between force and displacement – so work can be positive, negative or zero.

1. $\theta =0^{\circ }$ (force along motion) → positive work, e.g. pushing a trolley.
2. $\theta ={180}^{\circ }$ (force opposite motion) → negative work, e.g. friction.
3. $\theta ={90}^{\circ }$ → zero work.
4. Of the options, "either positive or negative" is correct; it is not always one sign.

Yaad rakhein: Force helps motion → +W; force opposes motion → −W.

Answer: (C) either positive or negative

Concept: A convex mirror always forms a virtual, erect and diminished image behind the mirror, between P and F.

1. As the object moves farther away, the image shrinks and moves towards F.
2. For an object at infinity, parallel rays reflect and appear to diverge from the focus F.
3. So the image is highly diminished, point-sized and virtual, located at F behind the mirror.

Trick: Convex mirror: object at $\infty$ → image at F (behind); any other position → between P and F.

Answer: (B) behind the mirror at the focus F

Concept: The plasma membrane is the selectively permeable outer boundary of every cell.

1. It is a lipid bilayer (mainly phospholipids).
2. Proteins are embedded in or attached to this bilayer (fluid mosaic model).
3. Cellulose is found in the plant cell wall, not in the membrane.

Yaad rakhein: Membrane = lipids + proteins (fluid mosaic); cell wall = cellulose.

Answer: (C) Both proteins and lipids

Concept: Variations arise mainly because DNA copying during reproduction is never 100% accurate.

1. Before cell division, the cell makes a copy of its DNA.
2. Small errors in this copying create slightly different DNA in offspring.
3. These variations help some individuals survive changing environments, aiding the species over time.

Yaad rakhein: Inaccurate DNA copying → variation → survival of species (NCERT Class 10).

Answer: (B) DNA copying

Concept: Oxidising agents add oxygen to alcohols and convert them into carboxylic acids.

1. Alkaline $\mathrm{K}\mathrm{M}\mathrm{n}{\mathrm{O}}_4$ (or acidified ${\mathrm{K}}_2\mathrm{C}{\mathrm{r}}_2{\mathrm{O}}_7$) is a strong oxidising agent.
2. $\mathrm{C}{\mathrm{H}}_3\mathrm{C}{\mathrm{H}}_2\mathrm{O}\mathrm{H}\stackrel{\mathrm{a}\mathrm{l}\mathrm{k}.\mathrm{K}\mathrm{M}\mathrm{n}{\mathrm{O}}_4+\mathrm{h}\mathrm{e}\mathrm{a}\mathrm{t}}{\to }\mathrm{C}{\mathrm{H}}_3\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{H}$
3. Pd and Ni are hydrogenation catalysts; Zn is a reducing metal.

Trick: Purple $\mathrm{K}\mathrm{M}\mathrm{n}{\mathrm{O}}_4$ loses its colour while it oxidises the alcohol.

Answer: (C) Alkaline potassium permanganate

Concept: The number of heart chambers differs among vertebrate groups.

1. Fishes: 2 chambers (1 atrium, 1 ventricle).
2. Amphibians and most reptiles: 3 chambers (2 atria, 1 ventricle), so some mixing of blood occurs.
3. Birds, mammals and crocodiles: 4 chambers.

Trick: Fish 2 → Frog 3 → Bird/Man 4.

Answer: (D) Three

Concept: Members of a homologous series have the same functional group and differ by a $-\mathrm{C}{\mathrm{H}}_2-$ unit.

1. $\mathrm{C}{\mathrm{H}}_3\mathrm{O}\mathrm{H}$, ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{O}\mathrm{H}$, ${\mathrm{C}}_3{\mathrm{H}}_7\mathrm{O}\mathrm{H}$ fit ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+1}\mathrm{O}\mathrm{H}$ — alcohols, each differing by $\mathrm{C}{\mathrm{H}}_2$.
2. ${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{O}\mathrm{H}$ (phenol) has –OH on a benzene ring, not on an alkyl chain.
3. It does not fit the general formula, so it is the odd one out.

Trick: Check the formula ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+1}\mathrm{O}\mathrm{H}$: for $n=6$ it should be ${\mathrm{C}}_6{\mathrm{H}}_{13}\mathrm{O}\mathrm{H}$, not ${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{O}\mathrm{H}$.

Answer: (D) ${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{O}\mathrm{H}$

Concept: Starlight passes through atmospheric layers of continuously changing density and refractive index.

1. Light from a star bends (refracts) repeatedly on entering the atmosphere.
2. Since the air is always moving, the amount of bending keeps changing.
3. So the amount of light reaching the eye flickers — the star twinkles.

Yaad rakhein: Twinkling, advance sunrise, delayed sunset → atmospheric refraction. Blue sky → scattering.

Answer: (B) the atmospheric refraction of light from the star

Concept: Voltage is work done per unit charge: $V=\frac{W}{Q}$.

1. Charge $Q=I\times t$.
2. Substitute: $V=\frac{W}{Q}=\frac{W}{I\times t}$.
3. So voltage $=\frac{\text{Work done}}{\text{Current}\times \text{Time}}$.

Trick: Units check: $\frac{\text{J}}{\text{A}·\text{s}}=\frac{\text{J}}{\text{C}}=\text{V}$.

Answer: (D) $\frac{\text{Work done}}{\text{Current}\times \text{Time}}$

Concept: Paramecium is a unicellular protozoan whose body is covered with cilia used for movement and feeding.

1. Amoeba is unicellular but moves by pseudopodia, not cilia.
2. Ticks (arthropods) and leeches (annelids) are multicellular.
3. So the unicellular ciliated organism is Paramecium.

Trick: Paramecium → cilia; Amoeba → pseudopodia; Euglena → flagellum.

Answer: (A) Paramecium

Concept: Evaporation is a surface phenomenon — only surface particles escape into vapour.

1. Larger surface area exposes more particles to the air.
2. More particles escape per second, so evaporation becomes faster.
3. That is why clothes are spread out to dry.

Yaad rakhein: Evaporation ↑ with surface area, temperature and wind speed; ↓ with humidity.

Answer: (B) increased

Concept: Saturated carbon compounds contain only single C–C bonds.

1. Alkanes (${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+2}$) have only single bonds — saturated.
2. Alkenes (e.g. ethylene ${\mathrm{C}}_2{\mathrm{H}}_4$) have a double bond — unsaturated.
3. Alkynes have a triple bond — unsaturated.

Trick: Alk-ane = all single bonds; -ene = double; -yne = triple.

Answer: (D) Alkane

Concept: Match each named reaction with its true example.

1. (a) Ethanol + conc. ${\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4$ → ethene is dehydration, not saponification — wrong.
2. (b) Ethanoic acid + ethanol (acid catalyst) → ester is esterification — correct.
3. (c) Ester + NaOH → sodium salt of acid is saponification, not dehydration — wrong.

Trick: (a) and (c) have their names swapped; only (b) is right.

Answer: (C) Only (b) is correct.

Concept: A metal is more reactive than all metals below it in the reactivity series.

1. Series (part): $\mathrm{K}>\mathrm{N}\mathrm{a}>\mathrm{C}\mathrm{a}>\mathrm{M}\mathrm{g}>\mathrm{A}\mathrm{l}>\mathrm{Z}\mathrm{n}>\mathrm{F}\mathrm{e}>\mathrm{P}\mathrm{b}>\mathrm{H}>\mathrm{C}\mathrm{u}>\mathrm{H}\mathrm{g}>\mathrm{A}\mathrm{g}>\mathrm{A}\mathrm{u}$.
2. K, Na and Ca are above copper — more reactive than Cu.
3. Silver is below copper, so Cu displaces Ag from $\mathrm{A}\mathrm{g}\mathrm{N}{\mathrm{O}}_3$ solution.

Trick: $\mathrm{C}\mathrm{u}+2\mathrm{A}\mathrm{g}\mathrm{N}{\mathrm{O}}_3\to \mathrm{C}\mathrm{u}(\mathrm{N}{\mathrm{O}}_3{)}_2+2\mathrm{A}\mathrm{g}$ proves $\mathrm{C}\mathrm{u}>\mathrm{A}\mathrm{g}$.

Answer: (B) Silver

Concept: Biodegradable materials are broken down by biological processes.

1. Decomposers — mainly bacteria and fungi — act on such wastes.
2. They break complex organic matter into simple substances that return to the soil.
3. Sunlight and wind are physical agents; viruses do not decompose waste.

Yaad rakhein: Biodegradable = broken down by microbes (bacteria, fungi); plastics are non-biodegradable.

Answer: (C) Bacteria

Concept: Use $v=u+at$ and $s=ut+\frac{1}{2}a{t}^2$ with retardation $a=-2{\text{m s}}^{-2}$.

1. Final $v=0$, $t=10\text{s}$: $0=u-2\times 10\Rightarrow u=20{\text{m s}}^{-1}$.
2. $s=20\times 10-\frac{1}{2}\times 2\times {10}^2=200-100=100\text{m}$.
3. Check: $s=\frac{u^2}{2a}=\frac{400}{4}=100\text{m}$.

Trick: Stopping uniformly: $s=\frac{1}{2}a{t}^2=\frac{1}{2}\times 2\times {10}^2=100\text{m}$ (reverse motion).

Answer: (D) 100 m

Concept: Sperms travel from the testes to the urethra through the vas deferens.

1. Cutting and tying the vas deferens (vasectomy) blocks this path.
2. So sperms cannot be transferred, though other functions remain.
3. Fallopian tube is a female organ; cutting it (tubectomy) blocks the egg.

Yaad rakhein: Vasectomy → vas deferens (male); Tubectomy → fallopian tube (female).

Answer: (C) vas deferens

Concept: Fine air particles scatter shorter wavelengths much more strongly than longer ones.

1. Among visible colours, blue has a short wavelength; red has the longest.
2. So blue light is scattered the most in the atmosphere.
3. This is why the clear sky appears blue.

Yaad rakhein: Most scattered = blue (sky blue); least scattered = red (danger signals, sunset).

Answer: (A) blue

Concept: Compressibility depends on the space between particles.

1. Solids: particles tightly packed — almost incompressible.
2. Liquids: little space — very slightly compressible.
3. Gases: large intermolecular spaces — highly compressible (e.g. CNG, LPG cylinders).

Trick: CNG/LPG cylinders store large gas volumes only because gases compress easily.

Answer: (C) The gaseous state