RRB Technician Grade III 2024, 2025 PYQs

Concept: Electrical conduction needs free (mobile) electrons.

1. Graphite: each C bonds to 3 others; the 4th electron is delocalised → conducts
2. Diamond: each C bonds to 4 others; no free electron → insulator
3. Both are covalent, not metallic or ionic

Yaad rakhein: Graphite is the only non-metal that is a good conductor — used as electrodes.

Answer: (A) Graphite has delocalized electrons; diamond does not

Concept: Only metals above hydrogen in the reactivity series displace H₂ from dilute acids.

1. Copper is below hydrogen in the reactivity series
2. So Cu cannot displace hydrogen from dilute HCl → no reaction

Yaad rakhein: Cu, Ag, Au, Pt do not react with dilute HCl.

Answer: (C) No reaction

Concept: $\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$ (New Cartesian signs); convex mirror image is virtual, behind mirror (v +).

1. $u=-40$ cm, $v=+8$ cm
2. $\frac{1}{f}=\frac{1}{8}-\frac{1}{40}=\frac{5-1}{40}=\frac{4}{40}=\frac{1}{10}$
3. $f=+10$ cm

Trick: Convex mirror focal length is always positive → eliminate −10 and $-\frac{20}{3}$ at once.

Answer: (B) + 10 cm

Concept: $\text{pH}=-\log [{\text{H}}^{+}]$, so $[{\text{H}}^{+}]={10}^{-\text{pH}}$ M.

1. pH = 3
2. $[{\text{H}}^{+}]={10}^{-3}\text{M}=1\times {10}^{-3}\text{M}$

Trick: pH n means $[{\text{H}}^{+}]=1\times {10}^{-n}$ — the number 3 goes in the power, not in front.

Answer: (B) 1×10−3 M

Concept: Action and reaction are equal in magnitude, opposite in direction and act on different bodies.

1. (i) says unequal and same direction → false
2. (ii) different bodies → true
3. (iii) same body → false
4. NOT true: (i) and (iii)

Yaad rakhein: Because they act on different bodies, action–reaction forces never cancel each other.

Answer: (A) Both (i) and (iii)

Concept: Meristematic cells are actively dividing cells responsible for growth.

1. They have thin cellulose walls, dense cytoplasm, prominent nucleus and no vacuoles
2. They keep dividing to form new cells → plant grows
3. Thick walls / differentiation belong to permanent tissues

Yaad rakhein: Meristem types: apical (length), lateral (girth), intercalary (at nodes/base of leaves).

Answer: (B) Continuously divide throughout life

Concept: Apical meristem increases length; lateral meristem increases girth (thickness).

1. Apical meristem: at root and shoot tips → length
2. Lateral meristem (cambium): on the sides → girth of stem/root

Trick: Lateral = side → width/girth; Apical = apex → length.

Answer: (C) Girth

Concept: Slope of a distance–time graph = speed.

1. Steeper slope → more distance per unit time
2. Slope A > slope B → speed of A > speed of B
3. Uniform motion means zero acceleration for both, so option D is wrong

Yaad rakhein: Distance–time slope = speed; velocity–time slope = acceleration.

Answer: (B) The speed of body A is greater than speed of body B.

Concept: Growing different crops one after another on the same land in a planned sequence.

1. Alternating cereals with legumes restores nitrogen naturally
2. Reduces pests and nutrient depletion → keeps soil fertile
3. Monocropping drains the same nutrients every season

Yaad rakhein: Legumes (pulses) have Rhizobium in root nodules that fix atmospheric nitrogen.

Answer: (A) Crop rotation

Concept: A rheostat is a variable resistor used to change current in a circuit.

1. Sliding the contact changes the length of wire in circuit → resistance changes
2. Source voltage stays the same; current changes
3. Fuse protects, ammeter measures current, voltmeter measures p.d.

Yaad rakhein: Ammeter in series, voltmeter in parallel, rheostat in series to control current.

Answer: (D) Rheostat

Concept: $\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$; real image of concave mirror is in front (v negative).

1. $u=-120$ cm, $v=-40$ cm
2. $\frac{1}{f}=-\frac{1}{40}-\frac{1}{120}=-\frac{3+1}{120}=-\frac{4}{120}$
3. $f=-30$ cm

Trick: Concave mirror f is negative → only −60 or −30; $f=\frac{uv}{u+v}=\frac{4800}{-160}=-30$.

Answer: (C) - 30 cm

Concept: Kharif crops grow in the rainy (monsoon) season; rabi crops in winter.

1. Kharif: sown June–July, e.g. paddy, maize, cotton
2. Rabi: sown Oct–Nov, harvested March–April, e.g. wheat, gram, mustard

Yaad rakhein: Rabi = winter: wheat, gram, peas, mustard.

Answer: (B) Winter season

Concept: Position is always stated relative to a fixed reference point called the origin.

1. Example: 'school is 2 km north of the station' — station is the origin
2. Displacement and final position are measured from this origin

Yaad rakhein: Motion is relative — the same object can be at rest for one observer and moving for another.

Answer: (A) Origin

Concept: Rough ER has ribosomes on its surface, which make proteins.

1. Ribosomes give RER its rough look → site of protein synthesis
2. Smooth ER (no ribosomes) makes lipids and detoxifies
3. DNA replication occurs in the nucleus

Trick: Rough = Ribosomes = pRotein; Smooth = Lipids.

Answer: (C) Protein synthesis

Concept: A food web is a network of interconnected food chains.

1. Each organism has several food options and predators
2. If one species declines, others can substitute → ecosystem stays balanced
3. Energy flows (not recycled); nutrients are recycled

Yaad rakhein: Energy flow in an ecosystem is unidirectional; only ~10% passes to the next trophic level.

Answer: (D) They allow multiple feeding relationships, ensuring balance.

Concept: Structural isomers have the same molecular formula but different structures.

1. Pentane and 2-methylbutane: both C₅H₁₂ → isomers
2. Butane and 2-methylpropane: both C₄H₁₀ → isomers
3. Benzene C₆H₆ vs cyclohexene C₆H₁₀ → different formulas, not isomers

Trick: First count C and H — different formula means not isomers.

Answer: (A) A and B only

Concept: Slope of a v–t graph = acceleration.

1. Straight line → constant slope → uniform acceleration
2. Curved line → slope keeps changing → non-uniform acceleration
3. Horizontal line → constant velocity

Trick: Straight = uniform, curved = non-uniform.

Answer: (D) Non-uniform acceleration

Concept: Areolar tissue fills spaces, supports organs and helps repair; fat storage is done by adipose tissue.

1. Areolar: between skin and muscle, around blood vessels, nerves, bone marrow
2. Functions: fills space inside organs, supports internal organs, helps tissue repair
3. Storing fat globules for insulation → adipose tissue

Yaad rakhein: Adipose tissue is found below the skin and between organs; acts as an insulator.

Answer: (B) Storing fat globules for insulation

Concept: Isobars are atoms of different elements with the same mass number.

1. Same mass number, different atomic numbers
2. Example: ${}^{40}\text{Ca}$ ($Z=20$) and ${}^{40}\text{Ar}$ ($Z=18$)
3. Same atomic number/protons = isotopes, not isobars

Trick: iso-BAR: Greek 'barys' = heavy → same mass number; iso-TOPE: 'topos' = place → same atomic number.

Answer: (B) Same mass number

Concept: Work done = change in kinetic energy = $\frac{1}{2}m(v^2-u^2)$.

1. 72 km/h = 20 m/s; 108 km/h = 30 m/s
2. $W=\frac{1}{2}\times 120\times ({30}^2-{20}^2)=60\times (900-400)$
3. $W=60\times 500=30000\text{J}=3.0\times {10}^4\text{J}$

Trick: km/h → m/s: multiply by $\frac{5}{18}$ (72 → 20, 108 → 30).

Answer: (A) 3.0 × 10⁴ J