RRB Technician Grade III 2024, 2025 PYQs

Concept: Only about 10% of energy passes from one trophic level to the next (Lindeman's 10% law).

Solution:

1. About 90% energy is lost as heat, respiration and waste at each level
2. After 4 levels only ~0.1% of producer energy remains — too little to support another level
3. Producers are not rare; decomposers act at all levels, not just top

Yaad rakhein: Energy flow in an ecosystem is unidirectional; the energy pyramid is always upright.

Answer: (B) Only 10% of energy passes to the next level

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

Solution:

1. $a=\frac{5-0}{10}=0.5{\text{m/s}}^2$
2. $m=\frac{F}{a}=\frac{100}{0.5}$
3. $=200$ kg

Trick: $m=\frac{Ft}{v}=\frac{100\times 10}{5}=200$ kg (impulse = change in momentum).

Answer: (B) 200 kg

Concept: Galvanisation = coating iron/steel with a thin layer of zinc to prevent rusting.

Solution:

1. Zinc layer blocks air and moisture
2. Zinc is more reactive, so it corrodes first and protects iron even if scratched
3. Tinning uses tin; electroplating is a general method using electricity

Yaad rakhein: G for Galvanise, Z for Zinc — 'GZ' pair; tin-coating is for food cans.

Answer: (A) Galvanisation

Concept: Xylem has tracheids, vessels, xylem parenchyma and xylem fibres, each with a role.

Solution:

1. Xylem parenchyma (only living part) stores food
2. Xylem fibres are dead, thick-walled cells → mechanical support
3. Water/mineral transport is done mainly by tracheids and vessels

Yaad rakhein: Of the 4 xylem elements, only xylem parenchyma is living.

Answer: (B) Supportive function

Concept: Cell shape and size are adapted to the specific job the cell does.

Solution:

1. Nerve cells are long and branched to carry messages
2. RBCs are biconcave discs to carry oxygen
3. All body cells of one organism have the same genome — so the last option is wrong

Yaad rakhein: Division of labour in multicellular organisms leads to specialised cells.

Answer: (A) Their structure is adapted to perform specific functions.

Concept: Metal loses electrons, non-metal gains them; ions are held by electrostatic attraction.

Solution:

1. Na (2,8,1) loses 1 e⁻ → Na⁺; Cl (2,8,7) gains it → Cl⁻
2. Both get noble-gas configuration
3. Strong attraction between Na⁺ and Cl⁻ makes NaCl stable (ionic, not covalent)

Trick: Metal + non-metal → transfer (ionic); non-metal + non-metal → sharing (covalent).

Answer: (A) Sodium donates one electron to chlorine, forming oppositely charged ions held by strong electrostatic forces.

Concept: Rays from infinity are parallel; a concave lens diverges them so they appear to come from the focus.

Solution:

1. Object at infinity → image at focus F₁ (same side)
2. Image is virtual and erect
3. Image is highly diminished (point-sized)

Yaad rakhein: A concave lens always gives a virtual, erect, diminished image for any object position.

Answer: (B) Virtual, erect, and highly diminished at the focus

Concept: After fertilisation, ovary → fruit and ovule → seed.

Solution:

1. Zygote inside the ovule forms the embryo; ovule becomes seed
2. Ovary ripens into fruit
3. Sepals, petals, stamens, stigma and style usually wither and fall

Trick: 'Ovary is bigger → fruit (bigger); ovule is smaller → seed (smaller)'.

Answer: (C) The ovary develops into a fruit while the ovule becomes a seed

Concept: Object between F₁ and 2F₁ of a convex lens → image beyond 2F₂.

Solution:

1. Image forms beyond 2F₂ on the other side
2. It is real and inverted
3. It is enlarged

Trick: Object between F and 2F ↔ image beyond 2F (they swap with object beyond 2F). Closer object (but beyond F) → bigger image.

Answer: (A) Enlarged, real, inverted

Concept: Striated (skeletal) muscles are voluntary and attached to bones.

Solution:

1. Striated muscles: long, cylindrical, multinucleate, light-dark bands, voluntary
2. Smooth muscle: involuntary (gut, blood vessels)
3. Cardiac: involuntary, heart only; tendon is connective tissue, not muscle

Yaad rakhein: Tendon joins muscle to bone; ligament joins bone to bone.

Answer: (C) Striated (skeletal) muscle

Concept: Non-degradable chemicals accumulate and increase in concentration at each trophic level.

Solution:

1. Pesticides like DDT are not broken down and get stored in fat
2. Their concentration rises step by step up the food chain
3. Humans are at the top trophic level → highest concentration

Yaad rakhein: This phenomenon is called biomagnification; it is why DDT levels are highest in top carnivores.

Answer: (D) They occupy the top trophic level in food chains

Concept: Cytoplasm is the fluid between nucleus and membrane that contains organelles.

Solution:

1. Stains like safranin/methylene blue colour the nucleus darkly
2. Cytoplasm takes a light stain
3. Cytoplasm holds organelles like mitochondria, ER, Golgi

Yaad rakhein: Onion peel has a cell wall; cheek cells do not — both have nucleus and cytoplasm.

Answer: (B) Cytoplasm

Concept: Pair each muscle type with its control: voluntary or involuntary.

Solution:

1. Skeletal muscle → voluntary (under our will)
2. Cardiac muscle → involuntary (beats on its own)
3. 'Striated' is a structure feature, not a control type

Yaad rakhein: Cardiac muscle is striated, branched and involuntary — it never tires.

Answer: (B) Involuntary

Concept: Chemical fertilisers mainly supply N, P and K.

Solution:

1. NPK = Nitrogen, Phosphorus, Potassium
2. These are major macronutrients needed in large amounts
3. Zn, Ca, Mg are needed but are not the main supply of fertilisers

Yaad rakhein: Urea is a common nitrogen fertiliser (about 46% N).

Answer: (C) Nitrogen

Concept: Combination reaction: two or more reactants → a single product.

Solution:

1. 2Cu + O₂ → 2CuO, NH₃ + HCl → NH₄Cl, CaO + H₂O → Ca(OH)₂ — one product each
2. CuO + H₂ → Cu + H₂O gives two products
3. It is a redox (displacement) reaction: CuO reduced, H₂ oxidised

Trick: Count products: more than one product → not combination.

Answer: (B) $\mathrm{C}\mathrm{u}\mathrm{O}+{\mathrm{H}}_2\stackrel{\text{Heat}}{\to }\mathrm{C}\mathrm{u}+{\mathrm{H}}_2\mathrm{O}$

Concept: $P=P_1+P_2$ and $f=\frac{1}{P}$ (in metres).

Solution:

1. $P=+4+(-6)=-2$ D
2. $f=\frac{1}{-2}=-0.5$ m
3. = −50 cm (diverging)

Trick: $f(\text{cm})=\frac{100}{P}$: $\frac{100}{-2}=-50$ cm.

Answer: (B) - 50 cm

Concept: Weeds are unwanted plants that compete with crops.

Solution:

1. They take water, nutrients, light and space meant for crops
2. This lowers crop growth and yield
3. So weeding (manual, weedicides like 2,4-D) is needed

Yaad rakhein: Weedicides are sprayed before weeds flower and set seeds.

Answer: (A) Weeds compete with crops for resources.

Concept: $\text{KE}=\frac{1}{2}m{v}^2$, so $\text{KE}\propto v^2$.

Solution:

1. Velocity doubles (5 → 10 m/s)
2. KE becomes $2^2=4$ times
3. $4\times 25=100$ J

Trick: Ratio method: ${\left(\frac{10}{5}\right)}^2\times 25=100$ J — no need to find m (which is 2 kg).

Answer: (B) 100 J

Concept: Boiling point rises with external pressure and falls with lower pressure.

Solution:

1. Hill stations: lower air pressure → water boils below 100°C
2. Pressure cooker: higher pressure → boils above 100°C, cooking faster
3. Boiling point clearly depends on external pressure

Yaad rakhein: A liquid boils when its vapour pressure equals the external pressure.

Answer: (A) Boiling point of a liquid increases with an increase in atmospheric pressure and decreases with a decrease in atmospheric pressure.

Concept: Mass number A = protons + neutrons (nucleons).

Solution:

1. A is always a whole number and differs for isotopes
2. A = 2Z only for some light elements (e.g. C-12, O-16)
3. Not for all: e.g. Na has Z = 11, A = 23 → statement C is false

Yaad rakhein: Isotopes: same Z, different A; isobars: same A, different Z.

Answer: (C) It is equal to twice the atomic number for all elements.