RRB Technician Grade III 2024, 2025 PYQs

Concept: Average atomic mass = Σ (isotope mass × fractional abundance).

1. $35\times \frac{25}{100}=8.75$
2. $37\times \frac{75}{100}=27.75$
3. Average = $8.75+27.75=36.5$ u

Trick: Answer lies closer to the more abundant isotope (37): $35+\frac{3}{4}\times 2=36.5$.

Answer: (D) 36.5 u

Concept: Impure metal is the anode, pure metal strip is the cathode, salt solution of the metal is the electrolyte.

1. Anode: impure copper — dissolves into solution
2. Cathode: thin pure copper strip — pure Cu deposits
3. Electrolyte: acidified copper sulphate; impurities settle as anode mud

Trick: Mnemonic 'AI–CP': Anode = Impure, Cathode = Pure.

Answer: (D) Impure copper block

Concept: Mass can neither be created nor destroyed in a chemical reaction: mass of reactants = mass of products.

1. Reactants: 5.6 g Na + 8.0 g Cl₂
2. Product NaCl = 5.6 + 8.0 = 13.6 g

Yaad rakhein: Law given by Lavoisier; just add masses of reactants.

Answer: (C) 13.6 g

Concept: A negative ion (anion) forms by gaining electrons; charge −2 means 2 electrons gained, valency 2.

1. Electrons are negative, so gaining 2 e⁻ gives charge −2
2. Example: $\text{O}+2e^{-}\to {\text{O}}^{2-}$ (valency 2)
3. Protons never change in ions; electrons are not in the nucleus

Yaad rakhein: Gain of e⁻ → negative ion (non-metals); loss of e⁻ → positive ion (metals).

Answer: (B) The element has gained 2 electrons.

Concept: A ray through (or directed towards) the principal focus emerges parallel to the principal axis after refraction.

1. Convex lens: ray through F → parallel to axis
2. Concave lens: ray heading towards F on the other side → parallel to axis
3. Reverse of: parallel ray → passes through / appears from F

Yaad rakhein: Ray through optical centre goes undeviated; parallel ray ↔ focus ray are reverses of each other.

Answer: (C) It emerges parallel to the principal axis after refraction.

Concept: Non-biodegradable chemicals (e.g. DDT) accumulate more at each higher trophic level.

1. They cannot be broken down or excreted, so they pass up the food chain
2. Top consumers (e.g. humans, eagles) get the highest concentration
3. Biodegradation = breakdown by microbes (opposite idea)

Yaad rakhein: Maximum concentration of such chemicals is found in top carnivores.

Answer: (A) Biological magnification

Concept: Prokaryotic cells are small and simple; eukaryotic cells are larger and complex.

1. Prokaryotes: no nuclear membrane, no membrane-bound organelles (e.g. bacteria)
2. Eukaryotes: true nucleus and membrane-bound organelles (e.g. plant, animal cells), generally larger

Yaad rakhein: Pro = 'before' nucleus (no true nucleus); Eu = 'true' nucleus.

Answer: (D) Larger and complex

Concept: Male gamete is small and motile; female gamete is large, non-motile and stores food.

1. Sperm: tiny, has a tail → moves to reach the egg
2. Egg (ovum): larger, stores food for the zygote, does not move

Yaad rakhein: In humans the ovum is the largest cell and the sperm one of the smallest.

Answer: (A) Male gamete is small and motile; and female gamete is larger and non-motile.

Concept: $P=VI$; with $V=IR$, $P=I^{2}R=\frac{V^2}{R}$.

1. $P=VI$ ✓
2. $P=I^{2}R$ ✓ (put $V=IR$)
3. $P=\frac{V^2}{R}$ ✓ (put $I=\frac{V}{R}$)
4. $P=\frac{R}{V^2}$ is the reciprocal of $\frac{V^2}{R}$ → incorrect

Trick: Check units: $\frac{R}{V^2}$ is not watt — it is 1/W.

Answer: (B) P=R/V2

Concept: For mirrors, $m=-\frac{v}{u}$.

1. $m=+\frac{1}{3}$, $u=-30$ cm
2. $v=-m\times u=-\frac{1}{3}\times (-30)=+10$ cm

Trick: Convex mirror image is always behind the mirror → v positive; only +10 or +90, and $v=\frac{u}{3}$ in size → 10.

Answer: (B) + 10 cm

Concept: Electrolytic refining is the most common method to purify metals like Cu, Zn, Ag, Sn, Ni, Au.

1. Impure metal = anode, pure metal strip = cathode
2. Pure metal deposits on cathode; impurities form anode mud
3. Distillation suits low-boiling metals (Zn, Hg); smelting is extraction, not refining

Yaad rakhein: Anode mud from copper refining contains precious metals like gold and silver.

Answer: (C) Electrolytic refining

Concept: Electrons revolve in fixed circular orbits (energy levels/shells) around the nucleus.

1. Orbits K, L, M, N have fixed energy
2. While in an orbit, an electron does not radiate energy
3. The nucleus contains protons and neutrons, not electrons

Yaad rakhein: Maximum electrons in a shell = $2n^2$ (K = 2, L = 8, M = 18).

Answer: (A) Moving in fixed circular orbits around the nucleus

Concept: Gas solubility in liquids decreases as temperature increases.

1. Heating gives gas molecules energy to escape from the liquid
2. Example: warm soda loses fizz faster; warm water holds less O₂ (fish suffer)
3. Gas solubility increases with pressure (Henry's law)

Yaad rakhein: Gases: more soluble at low temperature and high pressure.

Answer: (C) Decreases with increase in temperature

Concept: For uniform motion starting at t = 0, distance ∝ time → straight line through the origin.

1. At t = 0, distance covered = 0 → point (0, 0)
2. Equal distances in equal time → straight line of constant slope
3. Points like (0, 1) or (1, 1) are not compulsory

Yaad rakhein: s = vt has no constant term, so the graph starts at the origin.

Answer: (D) The origin

Concept: Fusion of male and female gametes is fertilisation; its product is the zygote.

1. Male germ cell (from pollen tube) fuses with egg in the ovule
2. Zygote → develops into embryo; ovule → seed; ovary → fruit
3. Stigma, pollen grain and ovule are structures, not products of fusion

Yaad rakhein: Zygote → embryo, ovule → seed, ovary → fruit.

Answer: (B) Zygote

Concept: For a concave mirror, the reflecting surface faces the object, so C and F lie in front of the mirror.

1. C is the centre of the sphere of which the mirror is a part
2. Concave: C in front (R = 2f, negative)
3. Convex: C and F lie behind the mirror

Yaad rakhein: R = 2f — C is twice as far from the pole as F.

Answer: (C) In front of the mirror

Concept: Epidermal cells of roots form long hair-like root hairs to absorb water and minerals.

1. Root hairs greatly increase surface area for absorption
2. Waxy cutin is on aerial parts (prevents water loss)
3. Aerenchyma is in aquatic plants; thickened corners = collenchyma

Yaad rakhein: Cutin on leaves/stems reduces water loss; desert plants have a thick cuticle.

Answer: (D) Long, hair-like extensions

Concept: $a=\frac{F}{m}$: equal forces on different masses give different accelerations.

1. Action and reaction act on two different bodies
2. Same F, bigger mass → smaller a (gun recoils slowly, bullet moves fast)
3. Forces on the same body would cancel — not the case here

Yaad rakhein: Gun–bullet: equal and opposite forces, but the light bullet gets a huge acceleration.

Answer: (C) Because each force acts on a different object, and the objects may have different masses

Concept: Addition reactions occur at double or triple bonds, i.e. in unsaturated hydrocarbons.

1. Alkenes (C=C) and alkynes (C≡C) both undergo addition, e.g. hydrogenation
2. Alkanes (only single bonds) give substitution reactions

Yaad rakhein: Hydrogenation of vegetable oils (Ni catalyst) is an addition reaction → vanaspati ghee.

Answer: (A) Both alkynes and alkenes

Concept: Veins carry blood at low pressure back to the heart, so valves stop backflow.

1. Arteries: thick elastic walls, blood at high pressure from heart → no valves needed
2. Veins: thin walls, low pressure, blood often flows against gravity → valves keep it one-way

Yaad rakhein: Pulmonary vein carries oxygenated blood; pulmonary artery carries deoxygenated blood.

Answer: (A) Veins carry blood at low pressure and need valves to prevent backflow