RRB Technician Grade III 2024-25 20 December 2024 Shift 2 GK Questions – with answers & solutions

Correct Answer: Option 1 — tracheid
Tracheid is a plant tissue, not an animal connective tissue. It is a dead, lignified, tube-like cell of the xylem that conducts water and minerals from the roots to the leaves and also gives mechanical support to the plant.
Connective tissue is an animal tissue whose cells are loosely spaced and embedded in an intercellular matrix. Its job is to connect, support, bind and pack other tissues and organs of the body.
❌ Why the other options are incorrect
✗ Bone — a hard, rigid connective tissue with a matrix of calcium and phosphorus salts; forms the skeleton and anchors muscles.
✗ Blood — a fluid connective tissue with a liquid matrix called plasma; transports gases, food, wastes and hormones.
✗ Cartilage — a solid but flexible connective tissue with a matrix of proteins and sugars; found in the nose, ear, trachea and larynx.
📌 SSC & Railway Exam Facts
• The four basic animal tissues are Epithelial, Connective, Muscular and Nervous.
• Areolar, adipose, bone, cartilage, blood, tendon and ligament are all connective tissues.
• Tendon joins muscle to bone; ligament joins bone to bone.
• Plant conducting tissues are xylem (water) and phloem (food); xylem has tracheids, vessels, xylem parenchyma and xylem fibres.
• Blood is the only connective tissue that is liquid; adipose tissue stores fat and acts as an insulator.

Correct Answer: Option 3 — Hypothalamus
The hypothalamus lies at the base of the brain and is the master controller of the endocrine system. When the blood level of growth hormone falls, the hypothalamus secretes Growth Hormone Releasing Hormone (GHRH), also called growth hormone releasing factor. GHRH travels to the anterior pituitary and stimulates it to secrete Growth Hormone (GH / Somatotropin).
This is a classic example of feedback regulation — the amount of hormone in the blood itself decides how much more will be released.
❌ Why the other options are incorrect
✗ Pancreas — a mixed gland; secretes insulin and glucagon to control blood sugar, not GHRH.
✗ Adrenal gland — secretes adrenaline (emergency hormone) and cortisol; it is controlled by the pituitary, it does not control it.
✗ Thyroid gland — secretes thyroxine, which regulates carbohydrate, protein and fat metabolism; it needs iodine and is itself stimulated by pituitary TSH.
📌 SSC & Railway Exam Facts
• The pituitary gland is called the master gland, but it is itself controlled by the hypothalamus.
• Excess GH in childhood causes gigantism; deficiency causes dwarfism; excess in adults causes acromegaly.
• The hypothalamus also controls body temperature, hunger, thirst and sleep.
• The pituitary is located in a bony cavity of the skull called the sella turcica.

Correct Answer: Option 4 — Endoplasmic reticulum
The Endoplasmic Reticulum (ER) is a large network of membrane-bound tubes and sheets spread through the cytoplasm. It performs two roles at once:
• As a passageway (channel) — it transports materials, especially proteins, between different parts of the cell and between the cytoplasm and the nucleus.
• As a manufacturing surface — RER (Rough ER) carries ribosomes and makes proteins, while SER (Smooth ER) makes lipids and steroids and detoxifies poisons and drugs in the liver.
Because it provides a huge surface area for these processes, ER is also called the cytoplasmic framework of the cell.
❌ Why the other options are incorrect
✗ Mitochondria — the powerhouse of the cell; releases energy as ATP by respiration. It does not transport material across the cell.
✗ Ribosome — only the site of protein synthesis; it is a tiny granule without a membrane, so it cannot act as a passageway.
✗ Plastids — found only in plant cells; chloroplasts perform photosynthesis and leucoplasts store starch, oil and protein.
📌 SSC & Railway Exam Facts
• ER was discovered by Keith Porter (1945).
• RER looks rough because ribosomes are attached; SER has no ribosomes.
• The membrane of ER is similar to the plasma membrane, and ER also helps in membrane biogenesis.
• Golgi apparatus packages and dispatches the material made by the ER.
• Lysosomes are the suicide bags, mitochondria the powerhouse, and ribosomes the protein factory of the cell.

Correct Answer: Option 3 — The autotrophs or the producers are at the first trophic level.
Each step of a food chain where energy transfer takes place is called a trophic level. The correct arrangement is:
• First trophic level (T1) — Producers / autotrophs (green plants, algae) that trap solar energy and convert it into chemical energy by photosynthesis.
• Second trophic level (T2) — Herbivores / primary consumers (deer, grasshopper).
• Third trophic level (T3) — Small carnivores / secondary consumers (frog, snake).
• Fourth trophic level (T4) — Larger carnivores / tertiary consumers (hawk, lion).
❌ Why the other options are incorrect
✗ Option 1 — herbivores at the second level are primary consumers, not secondary consumers.
✗ Option 2 — autotrophs, not heterotrophs, fix solar energy. Heterotrophs cannot make their own food.
✗ Option 4 — larger carnivores / tertiary consumers occupy the fourth trophic level, not the third.
📌 SSC & Railway Exam Facts
• The term trophic level was given by Raymond Lindeman.
• Only about 10% of energy passes to the next trophic level — the 10 per cent law of Lindeman.
• Because of this heavy loss, food chains usually have only 3 to 4 trophic levels.
• Energy flow in an ecosystem is unidirectional, while nutrients are recycled.
• Harmful chemicals like pesticides increase at each higher level — this is biomagnification.

Correct Answer: Option 4 — Pollen grain and ovule
Fertilisation is the fusion of the male gamete with the female gamete. In flowering plants:
• The pollen grain, produced in the anther of the stamen (male part), carries the male gamete.
• The ovule, present inside the ovary of the pistil/carpel (female part), contains the egg cell (female gamete).
• After pollination, the pollen grain germinates on the stigma and grows a pollen tube down the style to reach the ovule, where fusion (fertilisation) takes place and a zygote is formed.
Without these two, fertilisation is simply not possible — hence they are the essential reproductive parts.
❌ Why the other options are incorrect
✗ Sepal — the green outermost whorl; only protects the flower bud. It is a non-essential (accessory) whorl.
✗ Thalamus — the swollen tip of the flower stalk on which all floral whorls are attached; it takes no part in fusion.
✗ Petals — coloured and scented; they only attract insects for pollination, so they are also accessory parts.
📌 SSC & Railway Exam Facts
• Stamen = anther + filament; Pistil/Carpel = stigma + style + ovary.
• Essential whorls — androecium (stamens) and gynoecium (pistil); accessory whorls — calyx (sepals) and corolla (petals).
• After fertilisation, the ovule becomes the seed and the ovary becomes the fruit.
• Bisexual flower — both stamen and pistil present (e.g. hibiscus); unisexual flower — only one present (e.g. papaya, watermelon).
• In angiosperms double fertilisation occurs — one male gamete forms the zygote, the other forms the endosperm.

Correct Answer: Option 1 — Only C
An ecosystem has two components:
• Biotic components — all living things: producers (green plants), consumers (herbivores, carnivores, omnivores, parasites) and decomposers (bacteria, fungi).
• Abiotic components — all non-living physical and chemical factors: soil, water, air, light, temperature, humidity and minerals.
Checking each statement:
• A is wrong — living organisms are biotic, not abiotic.
• B is wrong — soil is abiotic, not biotic.
• C is correct — minerals are indeed abiotic.
So only statement C is correct.
❌ Why the other options are incorrect
✗ B and C — B wrongly calls soil a biotic component.
✗ Only B — soil is abiotic, so B by itself is false.
✗ Both A and C — A wrongly calls living organisms abiotic.
📌 SSC & Railway Exam Facts
• The term ecosystem was coined by A. G. Tansley (1935).
• Decomposers are also called saprophytes; they return nutrients to the soil.
• A garden, pond or aquarium is an artificial (man-made) ecosystem; a forest, lake or ocean is a natural ecosystem.
• Ocean is the largest ecosystem on Earth.
• The study of the interaction of organisms with their environment is called ecology.

Correct Answer: Option 3 — Mitochondria
Mitochondria are called the powerhouse of the cell because they carry out aerobic respiration and release energy stored in food in the form of ATP (Adenosine Triphosphate). ATP is the energy currency of the cell and is used for muscle contraction, protein synthesis and all other life processes.
Mitochondria are double-membrane organelles; the inner membrane is deeply folded into cristae, which greatly increases the surface area for ATP-generating reactions. They have their own DNA and ribosomes, so they can make some of their own proteins — hence they are called semi-autonomous organelles.
❌ Why the other options are incorrect
✗ Vacuoles — storage sacs for water, sap and wastes; they give turgidity and rigidity to plant cells but produce no energy.
✗ Plastids — plant organelles; chloroplast traps sunlight for photosynthesis (it is called the kitchen of the cell, not the powerhouse).
✗ Endoplasmic reticulum — transport channel and manufacturing surface for proteins and lipids, not an energy producer.
📌 SSC & Railway Exam Facts
• Lysosome — 'suicide bag', discovered by Christian de Duve; contains powerful digestive enzymes.
• Mitochondria were discovered by Altmann; the name was given by Carl Benda.
• Chloroplast — kitchen of the cell; Golgi body — dispatching/traffic centre; Ribosome — protein factory.
• Mitochondrial DNA is inherited only from the mother.
• RBCs of mammals have no mitochondria and no nucleus, so they respire anaerobically.

Correct Answer: Option 3 — It stimulates growth in all organs.
Growth Hormone (GH / Somatotropin) is secreted by the anterior lobe of the pituitary gland. Its main function is to regulate the growth and development of the body, stimulating growth in all organs — bones, cartilage, muscles and soft tissues — by increasing protein synthesis and cell multiplication.
Its secretion is controlled by GHRH from the hypothalamus.
❌ Why the other options are incorrect
✗ Option 1 — development of female sex organs is stimulated by oestrogen, secreted by the ovary.
✗ Option 2 — blood sugar level is regulated by insulin and glucagon from the pancreas.
✗ Option 4 — metabolism of carbohydrates, proteins and fats is regulated by thyroxine from the thyroid gland.
📌 SSC & Railway Exam Facts
• Deficiency of GH in childhood causes dwarfism; excess causes gigantism; excess in adults causes acromegaly.
• Oestrogen — female secondary sexual characters; Testosterone — male secondary sexual characters (from the testis).
• Insulin deficiency causes diabetes mellitus.
• Thyroxine deficiency causes goitre; iodised salt prevents it.
• Adrenaline from the adrenal gland is the fight-or-flight / emergency hormone.

Correct Answer: Option 3 — Plasmolysis
Plasmolysis is the shrinkage of the protoplasm (cell contents) away from the cell wall when a plant cell is placed in a hypertonic solution (a solution more concentrated than the cell sap). Water moves out of the cell by osmosis, the vacuole shrinks, and the plasma membrane pulls away from the rigid cell wall.
If the plasmolysed cell is put back into pure water or a hypotonic solution, water re-enters and the cell regains its shape — this reverse process is called deplasmolysis.
❌ Why the other options are incorrect
✗ Passive Transport — the general movement of substances along the concentration gradient without energy; plasmolysis is one specific result, not the name of the process asked.
✗ Diffusion — movement of particles from higher to lower concentration, but it does not require a semi-permeable membrane and does not describe shrinking of cell contents.
✗ Active Transport — movement against the concentration gradient using ATP, e.g. uptake of minerals by root hair cells.
📌 SSC & Railway Exam Facts
• Osmosis is the movement of water (solvent) through a semi-permeable membrane from a region of higher water potential to lower water potential.
• Hypotonic solution → cell swells (endosmosis, turgid); Isotonic → no change; Hypertonic → cell shrinks (exosmosis, plasmolysed).
• Plasmolysis proves that the cell is living and that the plasma membrane is semi-permeable.
• Salt sprinkled on vegetables or applied for pickling kills microbes by plasmolysis.
• Turgor pressure from water inside the vacuole keeps herbaceous plants erect; loss of it causes wilting.

Correct Answer: Option 2 — Amoeba
Amoeba is a unicellular protozoan with an irregular, constantly changing body shape. Because it has no definite plane of symmetry, its binary fission can occur in any plane — the nucleus divides first (karyokinesis) and then the cytoplasm (cytokinesis), producing two identical daughter cells.
❌ Why the other options are incorrect
✗ Leishmania — has a whip-like flagellum at one end, giving the cell a definite orientation, so binary fission occurs in a definite (longitudinal) plane.
✗ Hydra — not a protozoan; it is a multicellular cnidarian that reproduces asexually by budding and regeneration.
✗ Plasmodium — the malarial parasite; it reproduces by multiple fission (schizogony), producing many daughter cells at once, not simple binary fission in any plane.
📌 SSC & Railway Exam Facts
• Binary fission — one parent divides into two; multiple fission — one parent divides into many.
• Amoeba moves and captures food using pseudopodia (false feet); its mode of nutrition is holozoic.
• Leishmania causes kala-azar; Plasmodium causes malaria; Entamoeba histolytica causes amoebic dysentery.
• Budding — Hydra, yeast; Fragmentation — Spirogyra; Regeneration — Planaria; Spore formation — Rhizopus.
• Asexual reproduction produces offspring that are genetically identical to the parent (clones).

Correct Answer: Option 3 — Mouth - Oesophagus - Stomach
Food travels through the alimentary canal in a fixed order:
• Mouth (buccal cavity) — teeth chew the food and salivary amylase (ptyalin) in saliva begins the digestion of starch.
• Oesophagus (food pipe) — carries the bolus down to the stomach by wave-like muscular contractions called peristalsis.
• Stomach — gastric glands release HCl, pepsin and mucus; HCl makes the medium acidic and kills germs, pepsin digests proteins, and mucus protects the stomach lining.
After the stomach the food goes to the small intestine → large intestine → rectum → anus.
❌ Why the other options are incorrect
✗ Oesophagus - Stomach - Mouth — digestion cannot begin in the oesophagus, and food never returns to the mouth.
✗ Mouth - Stomach - Oesophagus — the oesophagus lies before the stomach, not after it.
✗ Oesophagus - Mouth - Stomach — food enters the body through the mouth first, not the oesophagus.
📌 SSC & Railway Exam Facts
• Complete path: Mouth → Oesophagus → Stomach → Small intestine → Large intestine → Rectum → Anus.
• Small intestine is the main site of digestion and absorption; it is the longest part (about 6 m) and has finger-like villi to increase surface area.
• Liver secretes bile, which emulsifies fats; bile is stored in the gall bladder.
• Pancreatic juice contains trypsin (protein), amylase (starch) and lipase (fat).
• Large intestine mainly absorbs water; the appendix is a vestigial organ attached to it.

Correct Answer: Option 2 — Menstrual cycle
The ovary is the female gonad. It performs two jobs: it produces the ova (eggs) and it secretes the female sex hormones oestrogen and progesterone.
These hormones control the menstrual cycle — the monthly thickening and shedding of the uterine lining (endometrium) — and also develop the female secondary sexual characters such as breast development, widening of the pelvis and the feminine voice.
❌ Why the other options are incorrect
✗ Stimulates pituitary glands — the pituitary is stimulated by the hypothalamus through releasing hormones; in fact the pituitary (FSH and LH) stimulates the ovary, not the reverse.
✗ Regulates metabolism — done by thyroxine from the thyroid gland.
✗ Stimulates growth in all organs — done by growth hormone from the pituitary gland.
📌 SSC & Railway Exam Facts
• The menstrual cycle lasts about 28 days; ovulation (release of the egg) occurs around the 14th day.
• Progesterone is the pregnancy-maintaining hormone; it prepares the uterus for implantation.
• Testis secretes testosterone, which controls male secondary sexual characters.
• Placenta acts as a temporary endocrine gland during pregnancy.
• FSH and LH are gonadotropic hormones released by the anterior pituitary.

Correct Answer: Option 3 — Collenchyma
Collenchyma is a simple permanent tissue whose living cells are irregularly thickened with cellulose and pectin at the corners, leaving very little intercellular space. This corner thickening makes the tissue strong yet flexible, so tendrils and the stems of climbers can bend and twist without breaking.
It is usually found below the epidermis in the stems and leaf stalks of dicot plants.
❌ Why the other options are incorrect
✗ Chlorenchyma — parenchyma containing chlorophyll; its job is photosynthesis, not flexibility.
✗ Parenchyma — thin-walled living cells that mainly store food and water and fill space; they provide little mechanical strength.
✗ Aerenchyma — parenchyma with large air cavities; it gives buoyancy to aquatic plants like water hyacinth.
📌 SSC & Railway Exam Facts
• Simple permanent tissues: Parenchyma, Collenchyma, Sclerenchyma.
• Sclerenchyma — dead, lignified, very thick-walled cells; makes plant parts hard and stiff (e.g. coconut husk, nut shells).
• Complex permanent tissues: Xylem and Phloem (conducting tissues).
• Meristematic tissue is the dividing tissue — apical (length), lateral (girth) and intercalary (at the base of leaves/internodes).
• Epidermis is a protective tissue; in deserts it is coated with a waxy cutin to check water loss.

Correct Answer: Option 4 — Chlorofluorocarbons
Chlorofluorocarbons (CFCs) are man-made compounds of carbon, chlorine and fluorine, used as refrigerants in refrigerators and air-conditioners, and as propellants in aerosol sprays and fire extinguishers.
CFCs are very stable, so they slowly rise to the stratosphere. There UV radiation breaks them down and releases chlorine free radicals, and a single chlorine atom can destroy thousands of ozone molecules in a chain reaction. This caused the sharp fall in ozone observed from the 1980s, including the ozone hole over Antarctica.
❌ Why the other options are incorrect
✗ Iodobromocarbons — not the chemical class blamed for the 1980s ozone decline; halons (bromine compounds) contribute, but CFCs were the main cause.
✗ Iodofluorocarbons — not a commercially used refrigerant/propellant responsible for ozone depletion.
✗ Chloroiodocarbons — not the recognised ozone-depleting industrial substance of that period.
📌 SSC & Railway Exam Facts
• Ozone (O₃) is formed in the stratosphere when UV rays split O₂ into free oxygen atoms which then combine with O₂.
• The ozone layer is a protective shield that absorbs harmful UV radiation, which causes skin cancer and cataract.
• The ozone hole over Antarctica was reported in 1985.
• The Montreal Protocol (1987) froze and then phased out CFC production; 16 September is celebrated as World Ozone Day.
• In the troposphere, ozone is a harmful pollutant; in the stratosphere, it is essential for life.

Correct Answer: Option 3 — Centrifugation
A colloid is a heterogeneous mixture in which the dispersed particles are 1–1000 nm in size — far too small to be trapped by filter paper, yet large enough to scatter light (Tyndall effect). Because they pass straight through a filter, ordinary filtration cannot separate them.
Centrifugation spins the mixture at a very high speed in a centrifuge. The heavier colloidal particles experience a large centrifugal force and are thrown to the bottom of the tube as a sediment, while the lighter dispersion medium stays above and is decanted off.
Everyday uses: separating cream from milk, squeezing water out of wet clothes in a washing machine, and testing blood and urine samples in diagnostic laboratories.
❌ Why the other options are incorrect
✗ Evaporation — used to recover a dissolved non-volatile solute (e.g. common salt) from its solution; it cannot pick colloidal particles out of a mixture.
✗ Filtration — separates an insoluble solid from a liquid (a suspension); colloidal particles are too small and pass through the pores of the filter paper.
✗ Distillation — separates a volatile liquid from a non-volatile solute, or two miscible liquids with different boiling points.
📌 SSC & Railway Exam Facts
• Particle size: true solution < 1 nm, colloid 1–1000 nm, suspension > 1000 nm.
• Tyndall effect = scattering of a light beam; shown by colloids and suspensions, never by a true solution.
• Milk is a colloid (an emulsion); its cream is separated by centrifugation.
• Colloids cannot be separated by filtration but can be separated by centrifugation.
• A colloid has two parts — the dispersed phase and the dispersion medium.

Correct Answer: Option 3 — The number of atoms of each element in a molecule
In a chemical formula, the small number written below and to the right of an element's symbol is called the subscript. It states how many atoms of that element are present in one molecule (or formula unit) of the substance. A subscript of 1 is never written — we write NaCl, not Na₁Cl₁.
For example, H₂SO₄ contains 2 hydrogen, 1 sulphur and 4 oxygen atoms. In Al₂(SO₄)₃ the subscript 3 outside the bracket multiplies everything inside it, giving 2 Al, 3 S and 12 O atoms — a favourite exam trap.
Do not confuse the subscript with the coefficient written in front of a formula: in 2H₂O the leading 2 counts whole molecules and is adjusted while balancing an equation, while the 2 in H₂ counts atoms and must never be changed.
❌ Why the other options are incorrect
✗ The charge of the ion — the charge of an ion is written as a superscript, e.g. Na⁺, Ca²⁺, SO₄²⁻, not as a subscript.
✗ The oxidation state of the element — oxidation state is shown by Roman numerals in brackets in the name, e.g. iron(III) chloride, or is calculated from the formula; the subscript does not give it.
✗ The mass of the compound — mass is obtained by adding the atomic masses of all the atoms (molecular mass in u); the subscript is only a count of atoms, not a mass.
📌 SSC & Railway Exam Facts
• Subscript = number of atoms; coefficient (written in front) = number of molecules.
• H₂O has 2 H + 1 O atoms; its molecular mass = 18 u.
• Ca(OH)₂ contains 1 Ca, 2 O and 2 H atoms.
• Charge is always a superscript: Cl⁻, SO₄²⁻, PO₄³⁻.
• A middle dot shows water of crystallisation: CuSO₄·5H₂O (blue vitriol), Na₂CO₃·10H₂O (washing soda).

Correct Answer: Option 1 — It has fixed volume but not fixed shape.
Matter exists in three common states — solid, liquid and gas — and the state is decided by the intermolecular force of attraction and the intermolecular space between its particles.
In a liquid the particles are held by moderate forces of attraction: strong enough to keep the particles together, so the volume stays fixed, but weak enough to let them slide over one another, so the liquid flows and takes the shape of its container. That is why 1 litre of water remains 1 litre whether it is poured into a bottle, a beaker or a bowl.
Liquids are also only slightly compressible, have densities lower than solids but far higher than gases, and show moderate diffusion — which is why gases dissolve in them (fish breathe the oxygen dissolved in water).
❌ Why the other options are incorrect
✗ It is hard — rigidity and hardness belong to solids, whose particles only vibrate about fixed positions and cannot flow.
✗ It has fixed shape and volume — this is the definition of a solid, not of a liquid.
✗ It is highly compressible — high compressibility belongs to gases, which have very large intermolecular spaces; that is why LPG and CNG can be compressed into cylinders.
📌 SSC & Railway Exam Facts
• Intermolecular force: solid > liquid > gas; intermolecular space and compressibility: gas > liquid > solid.
• Rate of diffusion: gas > liquid > solid.
• Fixed volume, no fixed shape → liquid; fixed shape and volume → solid; neither fixed → gas.
• Plasma and Bose–Einstein condensate (BEC) are the fourth and fifth states of matter.
• Liquids have fluidity, so both liquids and gases are together called fluids.

Correct Answer: Option 2 — In the nucleus
Ernest Rutherford (1911) bombarded a thin gold foil with fast-moving alpha (α) particles and observed that (i) most particles passed straight through, (ii) a few were deflected through small angles, and (iii) about 1 in 12,000 bounced straight back.
From these observations he concluded that an atom is mostly empty space, that all of its positive charge and almost its entire mass are packed into an extremely small central region which he named the nucleus, and that the electrons revolve around the nucleus in circular paths called orbits.
The nucleus is about 10⁻¹⁵ m across while the atom is about 10⁻¹⁰ m across — the atom is roughly 100,000 times bigger than its nucleus, and yet the nucleus carries nearly all the mass, because protons and neutrons are about 1836 times heavier than an electron.
❌ Why the other options are incorrect
✗ In the shells of electrons — an electron's mass is only about 1/1836 u, so all the shells together add almost nothing to the atom's mass.
✗ In the electron cloud — the "electron cloud" is a feature of the later quantum mechanical model, and electrons carry negligible mass in any case.
✗ It is equally distributed throughout — this was J. J. Thomson's plum-pudding (watermelon) model, which Rutherford's α-scattering experiment disproved.
📌 SSC & Railway Exam Facts
• Rutherford's gold foil (α-scattering) experiment discovered the nucleus of the atom.
• Rutherford is called the Father of Nuclear Physics; he received the Nobel Prize in Chemistry, 1908.
• Electron — J. J. Thomson, Proton — Goldstein/Rutherford, Neutron — James Chadwick (1932).
• Main defect of Rutherford's model: a revolving electron should radiate energy and spiral into the nucleus — corrected by Niels Bohr.
• Mass of a proton ≈ mass of a neutron ≈ 1 u; mass number = protons + neutrons.

Correct Answer: Option 4 — Sweating causes rapid evaporation, which absorbs heat from the body surface and cools the body.
Evaporation is the change of a liquid into vapour at any temperature below its boiling point, and it takes place only from the surface of the liquid. The particles that escape are those with the highest kinetic energy, and to escape they must absorb energy — the latent heat of vaporisation — from their surroundings.
On a hot day the skin releases sweat, which is mostly water. As this sweat evaporates, it takes the latent heat it needs from the body surface, leaving the skin cooler. This is known as cooling caused by evaporation.
Evaporation becomes faster with higher temperature, larger surface area, greater wind speed and lower humidity — which is exactly why sweating cools us poorly on a humid day and very well on a dry, windy one.
❌ Why the other options are incorrect
✗ The given statement is wrong — the statement is scientifically correct; sweating genuinely lowers body temperature.
✗ Sweating increases blood circulation and cools the body — the cooling comes from the evaporation of sweat, not from any change in blood circulation.
✗ Sweating increases the body's temperature — exactly the opposite happens; evaporation removes heat and lowers the temperature of the skin.
📌 SSC & Railway Exam Facts
• Latent heat of vaporisation of water = 22.5 × 10⁵ J/kg (2260 kJ/kg); latent heat of fusion of ice = 3.34 × 10⁵ J/kg.
• Water stays cool in an earthen pot (matka) because water evaporating through its pores takes latent heat from the pot.
• Cotton clothes are worn in summer because cotton absorbs sweat and spreads it for fast evaporation.
• Evaporation is a surface phenomenon and a cooling process; boiling happens throughout the liquid at a fixed temperature.
• Evaporation increases with temperature, surface area and wind speed, and decreases with humidity.

Correct Answer: Option 4 — Chalk powder in water
A suspension is a heterogeneous mixture in which the solute particles are larger than 1000 nm and do not dissolve but merely remain suspended in the medium. Its tests are: the particles are visible to the naked eye, they scatter light (Tyndall effect), they settle down on standing, and they can be separated by ordinary filtration. A suspension is therefore an unstable mixture.
Chalk powder (calcium carbonate, CaCO₃) stirred into water passes every one of these tests — it makes the water turbid, it can be filtered out on filter paper, and on keeping the tumbler still the chalk settles at the bottom. Muddy water, paint and slaked lime used for whitewashing are other standard examples.
❌ Why the other options are incorrect
✗ Solution of sugar in water — a true solution: particle size < 1 nm, homogeneous, transparent, does not show the Tyndall effect and cannot be filtered.
✗ Few drops of milk in water — milk is a colloid (an emulsion); its particles are 1–1000 nm, do not settle down and pass through filter paper.
✗ Oil in water — this is an emulsion, a colloid of one liquid dispersed in another liquid, not a suspension.
📌 SSC & Railway Exam Facts
• Particle size: true solution < 1 nm < colloid < 1000 nm < suspension.
• Tyndall effect is shown by colloids and suspensions, never by a true solution.
• Suspension particles settle on standing and can be filtered; colloidal particles do neither.
• Chalk is calcium carbonate (CaCO₃); marble and limestone have the same formula.
• Mixtures are of two kinds — homogeneous (true solution, alloy) and heterogeneous (suspension, colloid).

Correct Answer: Option 1 — anode mud
Electrolytic refining is the last step of metallurgy and gives the metal in a very pure (about 99.9%) form. The arrangement is fixed:
• Anode (+) — a thick block of the impure metal
• Cathode (−) — a thin strip of the pure metal
• Electrolyte — a water-soluble salt of the same metal (for copper, acidified CuSO₄ solution)
When current is passed, the impure metal at the anode dissolves into the electrolyte as ions and an equal amount of pure metal is deposited on the cathode. The impurities do not follow: the soluble impurities go into the solution, while the insoluble impurities fall below the anode as a sludge called anode mud (anode sludge).
This anode mud is commercially valuable — in copper refining it contains silver, gold, platinum and selenium, which are recovered from it.
❌ Why the other options are incorrect
✗ gangue — the earthy, unwanted impurity present in the ore itself (sand, clay, rock), removed during concentration of the ore, long before refining begins.
✗ electrolytic mud — not a standard chemistry term; the accepted name for the deposit under the anode is anode mud.
✗ cathode mud — nothing settles at the cathode; the cathode only gains a coating of pure metal and becomes thicker.
📌 SSC & Railway Exam Facts
• In electrolytic refining: anode = impure metal, cathode = pure metal, electrolyte = salt solution of that metal.
• The deposit below the anode is anode mud, a commercial source of Ag, Au and Pt.
• Copper, zinc, tin, nickel, silver, gold and aluminium are refined electrolytically.
• Roasting = heating a sulphide ore strongly in excess air; calcination = heating a carbonate ore in limited air.
• Impurity in an ore = gangue; the substance added to remove gangue as slag = flux.

Correct Answer: Option 2 — Milk of magnesia
A sol is the type of colloid in which a solid is the dispersed phase and a liquid is the dispersion medium — in short, solid in liquid. Milk of magnesia is finely divided solid magnesium hydroxide, Mg(OH)₂, dispersed in water, and it is the standard textbook example of a sol. (In medicine it is used as an antacid and a mild laxative.)
Every colloid is named from the pair dispersed phase in dispersion medium:
• Sol = solid in liquid — milk of magnesia, mud, ink
• Solid sol = solid in solid — coloured gemstone, milky glass
• Foam = gas in liquid — shaving cream, whipped cream, soap lather
• Emulsion = liquid in liquid — milk, face cream
❌ Why the other options are incorrect
✗ Rubber — foam rubber has a gas dispersed in a solid, which makes it a foam (solid foam), not a sol.
✗ Foam — by definition a gas dispersed in a liquid; here the dispersed phase is a gas, not a solid.
✗ Face cream — a liquid dispersed in a liquid, i.e. an emulsion, not a sol.
📌 SSC & Railway Exam Facts
• Sol = solid in liquid; gel = liquid in solid (cheese, butter, jelly).
• Aerosol = solid or liquid dispersed in a gas — smoke, fog, clouds, mist.
• Milk is an emulsion (liquid fat in water); butter is a gel.
• Milk of magnesia is Mg(OH)₂, an antacid that neutralises excess HCl in the stomach.
• Colloids show the Tyndall effect, cannot be separated by filtration, but can be separated by centrifugation.

Correct Answer: Option 2 — Vanilla essence
An olfactory indicator is a substance whose smell (odour) changes in acidic or basic medium — it is detected with the nose, not the eye. The three commonly quoted olfactory indicators are vanilla essence, onion and clove oil.
Vanilla essence keeps its characteristic sweet smell in an acidic solution, but in a basic solution (for example NaOH) its smell disappears. The same happens with onion — its pungent smell vanishes in a base and survives in an acid. This is why olfactory indicators are especially useful for visually impaired students working in a laboratory.
❌ Why the other options are incorrect
✗ Red litmus — a natural visual indicator obtained from lichens; red litmus turns blue in a base and stays red in an acid. It shows a colour change, not a change of smell.
✗ Phenolphthalein — a synthetic visual indicator: colourless in acid and pink in base.
✗ Methyl orange — another synthetic visual indicator: red in acid and yellow in base (orange when neutral).
📌 SSC & Railway Exam Facts
• Olfactory indicators: onion, vanilla essence and clove oil.
• Natural indicators: litmus (from lichens), turmeric, red cabbage and china rose (hibiscus) petals.
• Litmus: acid → red, base → blue; turmeric: base → red (why a curry stain on cloth turns red with soap).
• Phenolphthalein: acid → colourless, base → pink. Methyl orange: acid → red, base → yellow.
• Universal indicator gives the pH on a 0–14 scale: pH < 7 acidic, pH = 7 neutral, pH > 7 basic.

Correct Answer: Option 3 — Water
A soap is the sodium or potassium salt of a long-chain fatty acid, for example sodium stearate, C₁₇H₃₅COO⁻Na⁺. Every soap molecule has two completely different ends:
• A long hydrocarbon tail that is hydrophobic (water-hating) and oil-loving — it dissolves in grease and oil.
• A charged –COO⁻Na⁺ head that is hydrophilic (water-loving) — it is attracted to and dissolves in water.
So the hydrophilic end interacts with water. When soap is added to water carrying greasy dirt, the tails bury themselves inside the oil droplet while the heads point outwards into the water, forming a spherical cluster called a micelle. The dirt is trapped inside the micelle and is carried away with the rinse water.
❌ Why the other options are incorrect
✗ Hydrocarbon — the hydrocarbon (oil/grease) is attacked by the hydrophobic tail, not by the hydrophilic head.
✗ Both water and oil — the whole soap molecule acts on both, but the hydrophilic end alone interacts only with water; that is what the question asks.
✗ Oil — oil is dissolved by the non-polar hydrophobic tail; the charged hydrophilic head is repelled by oil.
📌 SSC & Railway Exam Facts
• Soap = sodium/potassium salt of a higher fatty acid; it is made by saponification: fat/oil + NaOH → soap + glycerol.
• The spherical cluster formed by soap molecules in water is called a micelle.
• Soap does not lather in hard water — Ca²⁺ and Mg²⁺ ions form an insoluble scum; detergents work even in hard water.
• Detergents are ammonium or sulphonate salts of long-chain hydrocarbons and are not readily biodegradable.
• Hydrophilic = water-loving head; hydrophobic = water-hating hydrocarbon tail.

Correct Answer: Option 2 — pure metal
In electrolytic refining, the impure metal obtained after reduction of the ore is purified by electrolysis. The set-up is fixed and is asked directly in exams:
• Anode (positive electrode) — a thick block of the impure metal
• Cathode (negative electrode) — a thin strip or sheet of the pure metal
• Electrolyte — an aqueous solution of a salt of the same metal, e.g. acidified CuSO₄ for copper
On passing current the anode dissolves — metal atoms lose electrons and enter the solution as ions (Cu → Cu²⁺ + 2e⁻) — and an equivalent amount of metal is reduced and deposited on the cathode (Cu²⁺ + 2e⁻ → Cu) in a very pure form. The insoluble impurities settle below the anode as anode mud.
So the cathode must be made of the pure metal; it keeps growing thicker as refining proceeds, while the anode gets thinner.
❌ Why the other options are incorrect
✗ impure metal — the impure metal is used as the anode, which dissolves away and becomes thinner during refining.
✗ alloy metal — an alloy would add fresh impurities to the deposit and defeat the very purpose of refining.
✗ metal salt — the salt is used as the electrolyte solution, not as an electrode; a solid salt is also a poor conductor of electricity.
📌 SSC & Railway Exam Facts
• Cathode = pure metal (reduction); anode = impure metal (oxidation).
• Electrode reactions: anode Cu → Cu²⁺ + 2e⁻; cathode Cu²⁺ + 2e⁻ → Cu.
• The anode mud below the anode contains valuable Ag, Au, Pt and Se.
• Reduction always occurs at the cathode and oxidation at the anode.
• Order of metallurgy: concentration of ore → roasting/calcination → reduction → refining.

Correct Answer: Option 4 — Alpha particles
An alpha (α) particle is a doubly-charged helium ion, He²⁺ — a helium atom that has lost both of its electrons. It therefore consists of 2 protons and 2 neutrons, carries a charge of +2 and has a mass of about 4 u, making it identical to the nucleus of a helium-4 atom.
Alpha particles are given out in radioactive alpha decay, in which the mass number falls by 4 and the atomic number by 2. Because they are heavy and doubly charged, they are the least penetrating of the three nuclear radiations — a sheet of paper or a few centimetres of air stops them — but they are the most ionising.
These are exactly the particles Rutherford fired at a thin gold foil in his famous scattering experiment that revealed the nucleus.
❌ Why the other options are incorrect
✗ Gamma particles — gamma (γ) rays are high-energy electromagnetic waves, not particles of matter; they have no mass and no charge.
✗ X-rays — also electromagnetic radiation, discovered by W. C. Roentgen; they are produced outside the nucleus and carry no charge.
✗ Beta particles — beta (β) particles are fast-moving electrons with a single negative charge (−1), released when a neutron changes into a proton inside the nucleus.
📌 SSC & Railway Exam Facts
• α = He²⁺ (helium nucleus), β = electron, γ = electromagnetic wave.
• Penetrating power: γ > β > α; ionising power: α > β > γ.
• α is stopped by paper, β by an aluminium sheet, γ needs thick lead or concrete.
• Radioactivity was discovered by Henri Becquerel; the α, β and γ rays were named by Rutherford (and γ by Villard).
• In α-decay: mass number −4, atomic number −2; in β-decay: mass number unchanged, atomic number +1.

Correct Answer: Option 3 — non-uniform acceleration
Acceleration is the rate of change of velocity with time, a = (v − u)/t. Its SI unit is m/s² and it is a vector quantity.
Acceleration is said to be uniform when the velocity changes by equal amounts in equal intervals of time, and non-uniform (variable) when the velocity changes by unequal amounts in equal intervals of time. In this question the car's speed rises by a different amount in every equal time interval, so the rate of change of velocity is itself changing — the car moves with non-uniform acceleration.
A car being driven through crowded city traffic, where the driver keeps pressing and releasing the accelerator, is the standard everyday example.
❌ Why the other options are incorrect
✗ uniform speed — this means the car covers equal distances in equal intervals of time; its speed would not change at all.
✗ uniform velocity — velocity constant in both magnitude and direction; acceleration would then be zero.
✗ uniform acceleration — this needs the speed to increase by equal amounts in equal intervals, e.g. a freely falling body.
📌 SSC & Railway Exam Facts
• Speed is a scalar, velocity is a vector; both have SI unit m/s.
• a = (v − u)/t; SI unit m/s².
• Free fall is the classic case of uniform acceleration, g = 9.8 m/s².
• Negative acceleration is called retardation or deceleration.
• For uniform acceleration the velocity–time graph is a straight line; for non-uniform acceleration it is a curve.

Correct Answer: Option 2 — Advance sunrise and delayed sunset
Atmospheric refraction is the bending of light as it passes through layers of air of continuously changing optical density. Air near the ground is denser (hotter and more compressed) than air higher up, so a ray coming from the Sun bends towards the normal as it enters denser layers and follows a curved path.
Because of this, the Sun is seen about 2 minutes before it actually rises above the horizon and continues to be seen about 2 minutes after it has actually set — giving an advanced sunrise and a delayed sunset, and lengthening the day by roughly 4 minutes. The twinkling of stars, the apparent flattening of the Sun's disc at sunrise/sunset and the advance apparent position of the Sun are all effects of the same phenomenon.
❌ Why the other options are incorrect
✗ Curved mirrors to form enlarged image of an object — this is reflection by a concave mirror, not refraction.
✗ Rainbow formation — caused by refraction, total internal reflection and dispersion of sunlight inside water droplets, not by the atmosphere's density layers.
✗ Image formation by plain mirrors — plane mirrors work purely by the laws of reflection; the image is virtual, erect and of the same size.
📌 SSC & Railway Exam Facts
• The day appears about 4 minutes longer because of atmospheric refraction.
• Twinkling of stars (stellar scintillation) is due to atmospheric refraction; planets do not twinkle because they are extended sources.
• The blue colour of the sky and the red colour of the rising/setting Sun are due to scattering, not refraction.
• Refractive index of air ≈ 1.0003; of water 1.33, of glass about 1.5, of diamond 2.42.

Correct Answer: Option 3 — backwards
This is a direct application of Newton's first law of motion, also called the law of inertia: a body at rest stays at rest and a body in motion keeps moving with the same velocity in a straight line unless an unbalanced external force acts on it.
When the bus is standing, our feet and our whole body are at rest. The moment the bus starts, the floor of the bus (and therefore our feet, which are in contact with it through friction) moves forward. The upper part of our body, however, still tends to remain at rest because of inertia of rest. As a result the feet go ahead while the upper body lags behind, and we fall backwards.
The opposite happens when a moving bus stops suddenly — the lower body stops, the upper body continues forward, and we lurch forward.
❌ Why the other options are incorrect
✗ left side — a sideways fall happens only when the bus takes a sharp turn, not while moving straight.
✗ right side — same reasoning; a straight start produces no sideways push.
✗ forward — we fall forward when a moving bus brakes suddenly (inertia of motion), which is the reverse situation.
📌 SSC & Railway Exam Facts
• Newton's first law defines force and inertia; it is also called Galileo's law of inertia.
• Inertia depends on mass — the greater the mass, the greater the inertia. Mass is a measure of inertia.
• Three kinds: inertia of rest, inertia of motion, inertia of direction.
• Dust flying off when a carpet is beaten, and a coin falling into a glass when the card below it is flicked, are examples of inertia of rest.
• Seat belts are provided in vehicles to counter the inertia of motion during sudden braking.

Correct Answer: Option 3 — v = 2π r/t
📖 Given
• Radius of the circular path = r
• Time taken for one complete round = t seconds
• Distance covered in one round = circumference of the circle
✍️ Formula
Speed = Total distance / Total time, and circumference of a circle = 2πr
🔢 Solution
• Distance covered in one round, s = 2πr
• Time taken, t = t seconds
• v = s/t
• v = 2πr/t
So an athlete running once round a circular track covers a length equal to the circumference 2πr, and dividing it by the time gives the uniform circular speed.
❌ Why the other options are incorrect
✗ v = π r² /t — πr² is the area of the circle, not its perimeter; area divided by time is not a speed.
✗ v = 2 m/s — a fixed numerical value cannot be the answer when r and t are unknown symbols.
✗ v = 0 — the displacement after one full round is zero, so the average velocity is zero, but the speed (distance/time) is not zero.
📌 SSC & Railway Exam Facts
• Circumference of a circle = 2πr; area = πr².
• In uniform circular motion the speed is constant but the velocity keeps changing because the direction changes continuously — hence it is an accelerated motion.
• The acceleration in circular motion is centripetal acceleration, a = v²/r, directed towards the centre.
• Distance is a scalar, displacement is a vector; in one full circle distance = 2πr but displacement = 0.
• Time for one complete revolution is called the time period (T); v = 2πr/T.

Correct Answer: Option 3 — Change in velocity per unit time - Acceleration
Acceleration is defined exactly as the change in velocity per unit time:
a = (v − u)/t, SI unit m/s², a vector quantity. So this pair is correctly matched.
The other three pairs are deliberately swapped. Uniform motion means the velocity does not change with time (equal distances in equal intervals), while non-uniform motion means the velocity keeps changing with time. A freely falling body falls under gravity alone, and since g = 9.8 m/s² is constant near the Earth's surface, its motion is a textbook case of uniform acceleration.
❌ Why the other options are incorrect
✗ Velocity does not change with time - Non-uniform motion — wrong pairing; unchanging velocity is uniform motion.
✗ Velocity varies with time - Uniform motion — wrong pairing; varying velocity is non-uniform (accelerated) motion.
✗ Motion of a freely falling body - Non-uniform acceleration — a freely falling body has uniform acceleration g, so the pairing is wrong.
📌 SSC & Railway Exam Facts
• v = u + at, s = ut + ½at², v² = u² + 2as are the three equations of motion for uniform acceleration.
• In uniform motion, average speed = instantaneous speed and the distance–time graph is a straight line.
• g = 9.8 m/s² (often taken as 10 m/s²) and is independent of the mass of the falling body.
• For a body thrown up, g is negative (retardation); while coming down it is positive.
• Slope of a velocity–time graph = acceleration; area under it = distance travelled.

Correct Answer: Option 3 — 0 m
📖 Given
• First motion: 15 m to the right of point A
• Second motion: 15 m in the opposite direction
• Final position = the same point A (the starting point)
✍️ Formula
Displacement = shortest distance between the initial and the final position (a vector)
Distance = total path length covered (a scalar)
🔢 Solution
• Take rightward as positive: first displacement = +15 m
• Leftward (opposite) displacement = −15 m
• Net displacement = (+15) + (−15)
• Displacement = 0 m
• Total distance covered = 15 + 15 = 30 m
Because the object finishes exactly where it started, its displacement is zero even though it has actually travelled 30 m.
❌ Why the other options are incorrect
✗ 30 m — this is the total distance (path length), obtained by adding both legs without their directions.
✗ 15 m — this is only one leg of the journey, not the net change of position.
✗ 7.5 m — this comes from wrongly averaging the two legs; displacement is never an average of distances.
📌 SSC & Railway Exam Facts
• Displacement ≤ Distance always; they are equal only for motion in a straight line without reversing.
• Displacement can be zero, positive or negative; distance is never negative.
• SI unit of both is the metre (m).
• In one complete circular round, distance = 2πr and displacement = 0.
• Average speed = total distance/total time, while average velocity = total displacement/total time — here the average velocity is 0.

Correct Answer: Option 1 — The magnitude of the magnetic field outside but close to the solenoid is extremely large.
A solenoid is a long cylindrical coil of many closely wound circular turns of insulated copper wire. When current flows through it, the field of every turn adds up inside the coil, so the field inside a long solenoid is strong and uniform, and the field lines there are parallel straight lines.
Outside the solenoid the field lines spread far apart, so the field there is extremely weak — practically zero for an ideal long solenoid. Hence the statement in Option 1 is incorrect and is the required answer.
The field of a solenoid is B = μ₀nI, where n is the number of turns per unit length. It can be increased by increasing the current, increasing the number of turns, or inserting a soft-iron core (which makes an electromagnet).
❌ Why the other options are incorrect (i.e. they are true statements)
✗ The solenoid in a way acts similar to the bar magnet — true; one end behaves as a north pole and the other as a south pole, and its field pattern matches that of a bar magnet.
✗ The strength of the magnetic field increases if we increase the number of turns — true; B ∝ n, so more turns per unit length give a stronger field.
✗ The magnetic field near the centre of long solenoid is nearly constant — true; the field in the central region of a long solenoid is uniform.
📌 SSC & Railway Exam Facts
• Field inside a long solenoid: B = μ₀nI; μ₀ = 4π × 10⁻⁷ T m A⁻¹.
• SI unit of magnetic field (magnetic flux density) is the tesla (T); smaller unit gauss, 1 T = 10⁴ gauss.
• The polarity of a solenoid is found by the right-hand thumb rule or the clock rule.
• A soft iron core is used in electromagnets because it is easily magnetised and demagnetised; steel is used for permanent magnets.
• Magnetic field lines never intersect, and they run from N to S outside and S to N inside a magnet.

Correct Answer: Option 1 — The iron rod would float on water surface.
When any object is placed in a fluid, two forces act on it: its weight (W = mg) acting vertically downwards, and the upthrust or buoyant force acting vertically upwards. By Archimedes' principle, the upthrust equals the weight of the fluid displaced by the object.
The behaviour of the object is decided by comparing these two forces:
Upthrust > Weight → the object floats; Upthrust = Weight → it just floats, fully submerged; Upthrust < Weight → it sinks.
The question specifically supposes that the upthrust is greater than the downward force. In that condition the net force on the rod is upwards, so the rod is pushed up and floats on the water surface — exactly as a ship made of iron does, because its hollow shape displaces a large volume of water.
❌ Why the other options are incorrect
✗ The iron rod would move downwards — a downward motion needs weight greater than upthrust, the opposite of the given condition.
✗ The iron rod would sink slowly — sinking of any kind requires a net downward force; here the net force is upward.
✗ The iron rod would sink faster — this would need an even larger weight compared with upthrust, which contradicts the given condition.
📌 SSC & Railway Exam Facts
• Archimedes' principle: upthrust = weight of fluid displaced.
• An object floats if its density is less than the density of the liquid; iron sinks in water because its density (7.8 g/cm³) exceeds water's (1 g/cm³).
• Upthrust increases with the volume of the object immersed and the density of the liquid.
• A hydrometer and a lactometer work on the principle of flotation; a ship floats because of its hollow shape.
• Ice floats on water because the density of ice (0.92 g/cm³) is less than that of water; about 1/10 of an iceberg stays above the surface.

Correct Answer: Option 3 — 10 m/s
📖 Given
• Initial velocity, u = 0 m/s (the car starts from rest)
• Uniform acceleration, a = 0.5 m/s²
• Time, t = 20 s
• To find: final velocity, v
✍️ Formula
v = u + at (first equation of motion)
🔢 Solution
• v = 0 + (0.5 × 20)
• v = 0 + 10
• v = 10 m/s
In plain language: the car gains 0.5 m/s of speed every second, so in 20 s it gains 0.5 × 20 = 10 m/s, and since it began from rest that gain is its final velocity.
❌ Why the other options are incorrect
✗ 5 m/s — this is what you get if you take t = 10 s instead of 20 s (0.5 × 10).
✗ 0 m/s — this is the initial velocity u, not the velocity after 20 s.
✗ 15 m/s — this comes from wrongly using a = 0.75 m/s² or t = 30 s; it does not follow from the given data.
📌 SSC & Railway Exam Facts
• The three equations of motion: v = u + at, s = ut + ½at², v² = u² + 2as.
• Distance covered here would be s = ut + ½at² = 0 + ½ × 0.5 × 400 = 100 m.
• SI unit of acceleration is m/s²; of velocity, m/s.
• Slope of a velocity–time graph = acceleration; area under it = distance.
• 1 m/s = 3.6 km/h, so 10 m/s = 36 km/h.

Correct Answer: Option 4 — Both 'A' and 'B' are correct.
Statement A is correct. The weight of a body is the force with which the Earth attracts it, W = mg. Since the gravitational pull of the Earth is directed towards its centre, weight always acts vertically downwards. Its SI unit is the newton (N) and it is measured with a spring balance.
Statement B is correct. Thrust is the force acting on a surface in a direction perpendicular (normal) to it. Its SI unit is also the newton (N). Thrust acting per unit area is called pressure, P = Thrust/Area, whose SI unit is the pascal (Pa), where 1 Pa = 1 N/m².
Since both statements match the standard definitions, the correct choice is that both A and B are correct.
❌ Why the other options are incorrect
✗ Both 'A' and 'B' are incorrect — wrong; both definitions are exactly as given in the textbook.
✗ 'A' is correct and 'B' is incorrect — B is also correct; thrust is by definition the perpendicular force on a surface.
✗ 'A' is incorrect and 'B' is correct — A is also correct; weight always acts vertically downwards towards the Earth's centre.
📌 SSC & Railway Exam Facts
• W = mg; mass is constant everywhere but weight changes with g.
• Weight on the Moon is 1/6 of that on the Earth because the Moon's g is about 1.63 m/s².
• Pressure = Thrust/Area; SI unit pascal (Pa) = N/m², named after Blaise Pascal.
• A sharp knife cuts better and a camel walks easily on sand because pressure decreases as the area increases.
• Atmospheric pressure at sea level = 1.013 × 10⁵ Pa = 1 atm ≈ 760 mm of Hg.

Correct Answer: Option 1 — parallel and equidistant straight lines
A magnetic field is said to be uniform when its magnitude and direction are the same at every point in the region. Magnetic field lines show both these properties at a glance: the direction of the tangent gives the direction of the field, and the closeness of the lines gives its strength.
Therefore, for a uniform field the lines must be straight and parallel (same direction everywhere) and equally spaced (same strength everywhere). This is exactly the pattern found inside a long current-carrying solenoid and in the central region between the poles of a large horseshoe magnet. The Earth's magnetic field over a small laboratory region is also treated as uniform.
❌ Why the other options are incorrect
✗ elliptical lines — curved lines mean the direction changes from point to point, so the field is non-uniform.
✗ parallel but irregular straight lines — the direction is the same but unequal spacing means the strength changes, hence non-uniform.
✗ concentric circular lines — this is the pattern around a straight current-carrying conductor, where the field decreases as distance from the wire increases (B ∝ 1/r), so it is non-uniform.
📌 SSC & Railway Exam Facts
• Magnetic field lines are closed continuous curves and never intersect each other.
• Outside a magnet they run from north to south; inside the magnet, from south to north.
• Field around a straight current-carrying wire: concentric circles, direction given by the right-hand thumb rule.
• B = μ₀nI inside a long solenoid gives a uniform field; SI unit tesla (T).
• Oersted (1820) discovered that a current-carrying conductor produces a magnetic field.

Correct Answer: Option 3 — Angle of prism
A glass prism is a transparent refracting medium bounded by two triangular bases and three rectangular lateral surfaces. The angle between its two refracting (lateral) faces on which light is incident and from which it emerges is called the angle of prism or the refracting angle, usually denoted by A. For the common equilateral prism used in the laboratory, A = 60°.
When a ray of white light passes through a prism it bends towards the base at both surfaces, and the angle between the direction of the incident ray and the emergent ray is the angle of deviation (D). Different colours are deviated by different amounts, which splits white light into its seven colours — the phenomenon of dispersion, first demonstrated by Sir Isaac Newton.
❌ Why the other options are incorrect
✗ Inclination angle — a general geometry term for the tilt of a line or plane; it is not used for the refracting angle of a prism.
✗ Base angle — the angle a lateral face makes with the base of the triangular face; light does not refract using this angle.
✗ Angle of deviation — the angle between the incident ray produced forward and the emergent ray; it is a property of the ray path, not of the prism's geometry alone.
📌 SSC & Railway Exam Facts
• Prism relation: A + D = i + e, where i is the angle of incidence and e the angle of emergence.
• At minimum deviation, i = e and the refracted ray inside the prism is parallel to the base.
• μ = sin[(A + D(m))/2] / sin(A/2) is the prism formula for refractive index.
• VIBGYOR — violet deviates the most, red the least, because violet has the shortest wavelength.
• Newton used a prism to obtain the spectrum and a second, inverted prism to recombine it into white light.

Correct Answer: Option 3 — 15 m
📖 Given
• Distance covered, s₁ = 25 m
• Time taken, t₁ = 5 s
• Motion is uniform, so the speed stays constant
• To find: distance s₂ covered in t₂ = 3 s
✍️ Formula
Speed = Distance / Time, i.e. v = s/t, and then s = v × t
🔢 Solution
• v = 25/5
• v = 5 m/s
• s₂ = v × t₂ = 5 × 3
• s₂ = 15 m
In plain language: Rambabu walks 5 metres every second, so in 3 seconds he will cover 5 × 3 = 15 m.
❌ Why the other options are incorrect
✗ 5 m — this is his speed in m/s (5 m/s), mistakenly written as the distance.
✗ 20 m — this comes from subtracting wrongly (25 − 5) instead of using speed × time.
✗ 10 m — this is what you get with t = 2 s (5 × 2), not 3 s.
📌 SSC & Railway Exam Facts
• In uniform motion a body covers equal distances in equal intervals of time, so acceleration = 0.
• Speed = distance/time; SI unit m/s, and 1 m/s = 3.6 km/h — so 5 m/s = 18 km/h.
• For uniform motion the distance–time graph is a straight line whose slope gives the speed.
• Average speed = total distance/total time; for uniform motion it equals the instantaneous speed.
• Distance is a scalar and displacement a vector; in straight-line motion without reversal they are equal.