RRB Technician Grade III 2024, 2025 PYQs

Concept: In a chemical reaction, total mass of reactants = total mass of products.

Solution:

1. CaCO₃ → CaO + CO₂.
2. 10 g = 5.6 g + mass of CO₂.
3. CO₂ = 10 − 5.6 = 4.4 g.

Trick: Molar check: 100 g CaCO₃ → 56 g CaO + 44 g CO₂; so 10 g gives 4.4 g.

Answer: (C) 4.4 g

Concept: Catenation and tetravalency let carbon form millions of compounds.

Solution:

1. Carbon bonds with itself (catenation) forming chains, branches and rings.
2. Valency 4 lets it bond with H, O, N, S, halogens.
3. These form the huge family of organic compounds.

Yaad rakhein: Catenation is strongest in carbon; silicon shows it only to a limited extent.

Answer: (A) Organic compounds

Concept: Turmeric is a natural indicator: yellow in acid/neutral, reddish-brown in base.

1. Turmeric (haldi) turns red/reddish-brown in basic solution — e.g. a haldi stain turns red with soap. So (B) is correct.
2. Red litmus turns blue in bases, not acids — (A) is wrong.
3. Methyl orange is a synthetic indicator, not obtained from turmeric — (C) is wrong.
4. China rose extract turns dark pink (magenta) in acids and green in bases — so 'green in acids' (D) is wrong.

Trick: China rose: acid → magenta, base → green; turmeric: base → red.

Answer: (B) Turmeric turns red in basic solution.

Concept: Echo travels to the surface and back: $v=\frac{2d}{t}$.

Solution:

1. Total distance = $2\times 990=1980$ m.
2. $v=\frac{1980}{6}=330$ m/s.

Trick: Forgetting the 2 gives 165 m/s — a trap option.

Answer: (C) 330 m/s

Concept: Weight F = mg, so F ∝ m on the same planet.

Solution:

1. F = mg = X.
2. Mass tripled → F = 3mg = 3X N.

Yaad rakhein: g does not depend on the body's own mass; only F (weight) changes.

Answer: (D) 3X N

Concept: Object beyond 2F → image between F and 2F, real, inverted, diminished.

Solution:

1. f = 40 cm → 2F = 80 cm; object at 100 cm is beyond 2F.
2. Image forms between F and 2F on the other side: 40–80 cm.
3. (Exact: $\frac{1}{v}=\frac{1}{40}-\frac{1}{100}\to v\approx 66.7$ cm, within range.)

Yaad rakhein: Object at 2F → image at 2F, same size; object between F and 2F → image beyond 2F, enlarged.

Answer: (C) The screen should be placed anywhere between 40 cm and 80 cm from the lens.

Concept: A molecule of two atoms of the same element is a homonuclear diatomic molecule.

Solution:

1. H₂: two H atoms ✓.
2. H₂O and CO contain different elements; O₃ has three atoms (triatomic).

Yaad rakhein: Diatomic elements: H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂.

Answer: (A) H₂

Concept: Meristems are growth tissues that keep dividing.

Solution:

1. Cells are small, thin-walled, with dense cytoplasm and prominent nucleus.
2. They lack (or have very small) vacuoles and divide actively.
3. Thick walls and storage are features of permanent tissues.

Yaad rakhein: Types: apical (length), lateral (girth), intercalary (at nodes/leaf base).

Answer: (C) Small, actively dividing cells with thin walls.

Concept: Colloids look homogeneous but are actually heterogeneous.

Solution:

1. 1 ✓: particles are tiny, so they appear uniform.
2. 2 ✗: at molecular level they are heterogeneous (dispersed phase + medium).
3. 3 ✓ Tyndall effect; 4 ✓ milk is an emulsion (colloid).

Trick: Eliminate statement 2 → only option without 2 is '1, 3 and 4 only'.

Answer: (D) 1, 3 and 4 only

Concept: Slope of v–t graph = acceleration.

Solution:

1. Horizontal line → slope 0 → acceleration 0.
2. Velocity stays the same → constant (uniform) velocity.

Yaad rakhein: Horizontal x–t graph = at rest; horizontal v–t graph = constant velocity.

Answer: (B) Constant velocity

Concept: $W=mgh$ when lifting a load.

Solution:

1. $W=10\times 10\times 2.5$.
2. $W=250$ J.

Yaad rakhein: Work against gravity = increase in potential energy (mgh).

Answer: (D) 250 J

Concept: Saturated hydrocarbons burn completely with a clean (blue) flame.

Solution:

1. Alkanes burn in air giving a clean, non-sooty blue flame.
2. Unsaturated hydrocarbons burn with a yellow, sooty flame (incomplete combustion).

Yaad rakhein: Saturated = clean blue flame; unsaturated = sooty yellow flame.

Answer: (A) Clean flame

Concept: Reactions that release heat are exothermic.

Solution:

1. C + O₂ → CO₂ + heat.
2. All combustion reactions release heat → exothermic.

Yaad rakhein: Burning, respiration and neutralisation are exothermic; photosynthesis is endothermic.

Answer: (C) Exothermic reaction

Concept: Plant cells have a cellulose cell wall; animal cells do not.

Solution:

1. Cell wall is outside the plasma membrane in plants.
2. Mitochondria, ER and cytoplasm are present in both.

Yaad rakhein: Plant-only: cell wall, plastids (chloroplasts), large central vacuole.

Answer: (A) Cell wall

Concept: Each trophic level depends on the level below for food.

Solution:

1. Herbivores are food for carnivores.
2. Fewer herbivores → less food → carnivore population falls.
3. Producers would not decrease from overgrazing because herbivores are fewer.

Yaad rakhein: Change at one level affects the next level up first.

Answer: (A) Carnivore population will decrease due to less food.

Concept: A concave lens always forms a virtual, erect, diminished image.

Solution:

1. For any real object position, rays diverge after refraction.
2. Image is always virtual, erect and between optical centre and F (same side).

Yaad rakhein: Object at infinity → image at F (highly diminished); otherwise between F and O.

Answer: (C) At any position in front of the lens.

Concept: $a=\frac{v-u}{t}$ in SI units.

Solution:

1. $v=216\times \frac{5}{18}=60$ m/s; $u=0$.
2. $t=10\text{min}=600\text{s}$.
3. $a=\frac{60}{600}=0.1$ m/s².

Trick: km/h → m/s: multiply by $\frac{5}{18}$ (216 → 60).

Answer: (C) 0.1 m/s2

Concept: Distance = area under velocity–time graph.

Solution:

1. Area = 10 m/s × 5 s (rectangle).
2. Distance = 50 m.

Yaad rakhein: Slope of v–t = acceleration; area under v–t = displacement.

Answer: (B) 50 m

Concept: $v=f\times \lambda$.

Solution:

1. f = 33 kHz = 33,000 Hz.
2. $v=33,000\times 0.01=330$ m/s.

Yaad rakhein: Ultrasound has frequency above 20 kHz but in air it still travels at sound speed (~330–343 m/s).

Answer: (C) 330 m/s

Concept: Criss-cross the valencies of the ions.

Solution:

1. Ca²⁺ and PO₄³⁻.
2. Cross valencies: Ca₃(PO₄)₂.
3. Check charge: $3\times (+2)=+6,2\times (-3)=-6$ ✓.

Trick: Swap the charge numbers: 2 goes to PO₄, 3 goes to Ca.

Answer: (B) Ca3(PO4)2