RRB Technician Grade III 2024-25 20 December 2024 Shift 3 GK Questions – with answers & solutions

Correct Answer: Option 1 — Ovary
After fertilisation, the zygote formed inside the ovule divides repeatedly to form the embryo. The ovule then develops a tough coat and becomes the seed, while the ovary of the flower grows rapidly and ripens to form the fruit. The remaining floral parts — sepals, petals, stamens, style and stigma — usually wither and fall off.
The ovary is the swollen basal part of the pistil (carpel), the female reproductive organ of the flower. The wall of the ovary thickens into the pericarp, the fleshy or hard covering of the fruit that protects the seeds and helps in their dispersal.
❌ Why the other options are incorrect
✗ Pollen tube — grows out of a germinating pollen grain and travels down the style only to deliver the male gamete to the ovule; it is consumed in the process and never becomes a fruit.
✗ Stigma — the sticky top of the pistil that receives pollen grains during pollination; it dries up after fertilisation.
✗ Anther — the pollen-bearing part of the stamen (male whorl) that produces pollen grains; it plays no role in fruit formation.
📌 SSC & Railway Exam Facts
• Ovary → fruit and ovule → seed after fertilisation — a classic PYQ pairing.
• Pistil / Carpel = stigma + style + ovary; Stamen = anther + filament.
• A fruit formed without fertilisation is a parthenocarpic fruit, e.g. banana.
• Fruits developing from parts other than the ovary are false fruits, e.g. apple (from the thalamus).
• Angiosperms show double fertilisation — one male gamete makes the zygote, the other makes the endosperm.

Correct Answer: Option 3 — fore-brain
The fore-brain is the main thinking part of the brain. Its largest region, the cerebrum, has separate sensory areas that receive impulses from receptors for hearing, smell, sight and touch, separate association areas where this information is interpreted and combined with earlier memory, and motor areas that send instructions to voluntary muscles.
The fore-brain also contains centres for hunger, thirst, emotions and body temperature in the hypothalamus. Thus thinking, reasoning, memory, intelligence and voluntary action are all controlled here.
❌ Why the other options are incorrect
✗ mid-brain — controls involuntary reflexes such as changes in pupil size and reflex movements of the head, neck and eyes; it does no thinking.
✗ hind-brain — has the cerebellum (precision of voluntary action, posture and balance), the pons, and the medulla (involuntary control of blood pressure, salivation, vomiting).
✗ spinal cord — a nerve cord that carries impulses to and from the brain and is the centre of reflex arcs; it does not think.
📌 SSC & Railway Exam Facts
• The brain has three parts — fore-brain, mid-brain and hind-brain.
• The cerebrum is the largest part of the human brain; the cerebellum is the second largest.
• The medulla oblongata controls breathing, heartbeat, coughing and sneezing.
• The brain is protected by the cranium (skull) and by three membranes called meninges, cushioned by cerebrospinal fluid (CSF).
• Reflex actions are completed by the spinal cord without waiting for the brain's decision.

Correct Answer: Option 3 — Only a few multicellular organisms
Fragmentation is a method of asexual reproduction in which the body of a multicellular organism breaks up into two or more fragments on maturing, and each fragment then grows into a new complete individual.
It is possible only in a few multicellular organisms with a simple body organisation, such as the filamentous alga Spirogyra and in Planaria. In organisms with complex body design and specialised organ systems — like human beings or higher plants — a broken piece cannot rebuild the whole body, so fragmentation does not occur. Unicellular organisms have only one cell, so they reproduce by binary or multiple fission, not by fragmentation.
❌ Why the other options are incorrect
✗ In all unicellular organisms — unicellular forms such as Amoeba, Paramecium and bacteria divide by fission, not fragmentation.
✗ Only in few unicellular organisms — fragmentation is by definition a multicellular phenomenon; a single cell has nothing to fragment into new bodies.
✗ In all multicellular organisms — complex multicellular organisms with specialised tissues and organs (e.g. mammals) cannot reproduce by fragmentation.
📌 SSC & Railway Exam Facts
• Spirogyra simply breaks into smaller pieces on maturation — the textbook example of fragmentation.
• Regeneration (Planaria, Hydra) differs from fragmentation — it restores a lost body part from specialised cells.
• Binary fission — Amoeba, Leishmania (longitudinal); Multiple fission — Plasmodium.
• Budding — Hydra and yeast; Spore formation — Rhizopus; Vegetative propagation — potato, Bryophyllum.
• Asexual reproduction produces clones — offspring genetically identical to the parent.

Correct Answer: Option 1 — Transpiration
Transpiration is the loss of water in the form of vapour from the aerial parts of a plant, mainly through the stomata of the leaves. As water evaporates from the leaf cells, a suction pull (transpiration pull) is created in the xylem column. Because water molecules stick to one another by cohesion and to the xylem walls by adhesion, this pull drags a continuous column of water upward from the roots to the leaves, and also helps the root hairs absorb more water and dissolved minerals from the soil.
Transpiration also cools the plant and helps in the upward transport of minerals.
❌ Why the other options are incorrect
✗ Photosynthesis — the process by which green plants make glucose from CO₂ and water using chlorophyll and sunlight; it consumes water but does not lift it.
✗ Translocation — the transport of prepared food (sucrose) from leaves to other parts through the phloem, using energy from ATP; direction is both upward and downward.
✗ Respiration — the oxidation of food to release energy (ATP) in the mitochondria; it has no role in water conduction.
📌 SSC & Railway Exam Facts
• Xylem carries water and minerals upward; phloem carries food in all directions.
• Transpiration is called a necessary evil — most absorbed water is lost, yet the pull is essential.
• About 90–95% of transpiration takes place through stomata; the rest is cuticular and lenticular.
• Guard cells open and close the stomata by becoming turgid or flaccid.
• Root pressure works mainly at night; transpiration pull is the major force during the day.

Correct Answer: Option 1 — Ureter
The human excretory system consists of two kidneys, two ureters, one urinary bladder and one urethra. Urine produced by the nephrons (the functional units of the kidney) is collected in the renal pelvis and is then carried away by a long muscular tube called the ureter.
Each ureter runs from the hilum of the kidney down to the urinary bladder, pushing urine along by peristalsis. The bladder stores the urine until it is expelled through the urethra during micturition.
❌ Why the other options are incorrect
✗ Pelvis (renal pelvis) — the funnel-shaped cavity inside the kidney itself that collects urine from the collecting ducts; it does not connect two organs.
✗ Urethra — the tube that carries urine from the urinary bladder to the outside of the body, not from the kidney.
✗ Penis — a male reproductive organ through which the urethra passes in males; it is not a link between kidney and bladder.
📌 SSC & Railway Exam Facts
• The nephron is the structural and functional unit of the kidney; each kidney has about 1 million nephrons.
• Filtration takes place in the glomerulus inside the Bowman's capsule — together called the Malpighian body.
• Urea is made in the liver from ammonia and is removed by the kidneys; human urine is about 95% water.
• An artificial kidney works on the principle of dialysis; the kidney is located in the abdominal cavity on either side of the backbone.
• Skin, lungs and liver are also excretory organs; in plants, excess water is removed by transpiration and guttation.

Correct Answer: Option 1 — Nucleus
In eukaryotic cells the nucleus is surrounded by a double-layered nuclear membrane (nuclear envelope) that separates it from the cytoplasm. This membrane bears nuclear pores through which materials move between the nucleus and the cytoplasm.
The nucleus contains chromatin, made of DNA and protein, which condenses into chromosomes at the time of cell division. DNA carries the genes that control heredity and direct the making of proteins and enzymes. Because every activity of the cell depends on these proteins, the nucleus is called the control centre or director of the cell; it also controls cell division.
❌ Why the other options are incorrect
✗ Endoplasmic reticulum — a single-membrane network that acts as a transport channel and a surface for making proteins (RER) and lipids (SER); it does not direct the cell.
✗ Plastids — double-membrane organelles found only in plant cells; chloroplasts carry out photosynthesis and leucoplasts store food.
✗ Ribosome — a tiny membrane-less granule of RNA and protein; it is only the site of protein synthesis.
📌 SSC & Railway Exam Facts
• The nucleus was discovered by Robert Brown (1831).
• Prokaryotes (bacteria, blue-green algae) have no nuclear membrane; their DNA lies in a nucleoid.
• The nucleolus inside the nucleus makes ribosomes; it is not membrane-bound.
• Human beings have 46 chromosomes (23 pairs); mature RBCs have no nucleus.
• Mitochondria and plastids are the other double-membrane organelles and have their own DNA.

Correct Answer: Option 2 — Increases absorptive surface area
The inner lining of the small intestine has millions of tiny finger-like projections called villi. Their main job is to increase the surface area for absorption of digested food. A larger surface means much more food can be absorbed in the same length of intestine.
Each villus is richly supplied with blood capillaries and a lymph vessel (lacteal). Glucose and amino acids pass into the blood capillaries, while fatty acids and glycerol are absorbed by the lacteal. The absorbed food is then carried by blood to every cell of the body, where it is used for energy, growth and repair.
❌ Why the other options are incorrect
✗ Secretion of minerals — minerals are absorbed from food, not secreted by villi; digestive juices are secreted by glands, not villi.
✗ Helps in excretion — excretion of nitrogenous waste is done by the kidneys; undigested food is removed by the large intestine and anus.
✗ Protection from acid — the stomach wall is protected from HCl by mucus, not by villi; the acidic food entering the duodenum is neutralised by alkaline bile and pancreatic juice.
📌 SSC & Railway Exam Facts
• The small intestine is the longest part of the alimentary canal (about 6–7 m) and the main site of digestion and absorption.
• It receives bile from the liver, pancreatic juice from the pancreas and intestinal juice from its own walls.
• Bile does not contain enzymes; it makes the medium alkaline and emulsifies fats.
• Trypsin digests proteins and lipase digests fats in the pancreatic juice.
• The large intestine mainly absorbs water; vitamin K and B₁₂ are also produced there by bacteria.

Correct Answer: Option 1 — connective tissue
This is an analogy question. Blood is a connective tissue — a fluid one, whose matrix is the liquid plasma. Bone is also a connective tissue, but a hard and rigid one, so the same relationship holds.
Connective tissue is defined by loosely spaced cells embedded in an intercellular matrix; the nature of the matrix decides the type. In bone the matrix is hard because it is rich in calcium and phosphorus salts. Bone forms the skeleton, supports the body, protects delicate organs such as the brain and lungs, and anchors the muscles.
❌ Why the other options are incorrect
✗ Epithelial tissue — a covering and lining tissue with tightly packed cells and almost no matrix; it forms the skin surface, the lining of the mouth, alveoli and kidney tubules.
✗ Nervous tissue — made of neurons, specialised to receive and conduct impulses; it forms the brain, spinal cord and nerves.
✗ Muscular tissue — made of contractile fibres that bring about movement; it is of three types — striated, smooth and cardiac.
📌 SSC & Railway Exam Facts
• The four animal tissues are epithelial, connective, muscular and nervous.
• Connective tissues include bone, cartilage, blood, lymph, tendon, ligament, areolar and adipose tissue.
• Tendon joins muscle to bone; ligament joins bone to bone.
• An adult human has 206 bones; cartilage is softer and is found in the nose, ear and trachea.
• Adipose tissue stores fat and acts as an insulator; blood is the only fluid connective tissue.

Correct Answer: Option 2 — Hydra
Hydra is a simple multicellular animal that reproduces asexually by budding. It uses regenerative cells — undifferentiated, actively dividing cells of its body wall — to produce a bud, which appears as a small outgrowth on one side of the parent body.
The bud grows, develops a mouth and tentacles, and finally detaches from the parent to live as a new independent individual. Since the bud is formed from the parent's own body cells, the new Hydra is genetically identical to the parent.
❌ Why the other options are incorrect
✗ Leishmania — a unicellular protozoan (causes kala-azar) that reproduces by binary fission in a definite longitudinal orientation with respect to its whip-like flagellum.
✗ Yeast — a unicellular fungus that also shows budding, but it uses a simple nuclear division of its single cell, not regenerative cells of a multicellular body.
✗ Amoeba — reproduces by binary fission, splitting into two daughter cells in any plane; it does not bud.
📌 SSC & Railway Exam Facts
• Budding — Hydra, yeast, *Sycon*; Regeneration — Hydra and Planaria.
• Binary fission — Amoeba, Paramecium, Leishmania; Multiple fission — Plasmodium (causes malaria).
• Spore formation — Rhizopus (bread mould); Fragmentation — Spirogyra.
• Hydra belongs to the phylum Coelenterata (Cnidaria) and also reproduces sexually in unfavourable conditions.
• Regeneration is carried out by specialised cells that proliferate and differentiate into various cell types.

Correct Answer: Option 2 — Plastic made material
Plastic is a man-made polymer that decomposers such as bacteria and fungi cannot break down, so it is non-biodegradable. Discarded plastic either stays inert in the environment for hundreds of years or releases harmful substances that damage the various members of the ecosystem — it chokes drains, kills cattle and marine animals that swallow it, and its additives enter food chains.
Because it does not decompose, plastic also accumulates through the food chain and cannot be returned to the soil as nutrients, unlike biodegradable waste.
❌ Why the other options are incorrect
✗ Paper made material — made from cellulose of wood; micro-organisms digest cellulose, so paper is biodegradable and can also be recycled.
✗ Clay made material — clay is a natural earth material; broken clay objects mix back into the soil and are not a persistent toxic pollutant like plastic.
✗ Plant leaves made material — leaves are purely organic and are quickly turned into humus by decomposers; they are the classic example of biodegradable waste.
📌 SSC & Railway Exam Facts
• Biodegradable — food waste, paper, cotton, leaves, cow dung; Non-biodegradable — plastic, glass, metal, DDT, polythene.
• The build-up of non-degradable chemicals at higher trophic levels is called biomagnification.
• Waste management follows the 4 R's — Refuse, Reduce, Reuse, Recycle.
• Vermicomposting uses earthworms to convert biodegradable waste into manure.
• 5 June is celebrated as World Environment Day.

Correct Answer: Option 3 — losing the fertile top-soil
Kulhads are disposable cups moulded from clay. Clay for pottery is dug out from the top-soil — the uppermost layer of soil that is rich in humus and minerals and supports plant growth. If kulhads are manufactured on a very large scale, enormous quantities of this fertile top-soil would be removed, which is why the practice cannot be considered environment-friendly.
Top-soil takes hundreds of years to form, so its loss means reduced soil fertility and greater risk of soil erosion. Hence the NCERT conclusion: for a very large population, disposable paper cups are a better option than kulhads.
❌ Why the other options are incorrect
✗ choking the sewage line — this is the typical problem of plastic and polythene waste, not of clay cups, which break up and settle.
✗ large remains collected in environment — clay is a natural earth material that merges back into the soil; it does not pile up as persistent waste.
✗ Unhygienic of its use — kulhads are actually hygienic, because each cup is used only once and then discarded.
📌 SSC & Railway Exam Facts
• Disposable plastic/thermocol cups are non-biodegradable, whereas paper cups are biodegradable.
• Top-soil is the most fertile layer, rich in humus, and is protected by vegetation cover.
• Removal of top-soil leads to soil erosion and desertification.
• The 4 R's of waste management are Refuse, Reduce, Reuse and Recycle.
• Reuse (e.g. refilling glass jars) is even better than recycling, because recycling itself needs energy.

Correct Answer: Option 3 — pistil (carpel)
In angiosperms (flowering plants) the reproductive parts are contained in the flower. The female reproductive part is the pistil or carpel, which occupies the centre of the flower and is made of exactly three parts:
• Stigma — the sticky top that receives the pollen grains during pollination.
• Style — the slender tube through which the pollen tube grows down.
• Ovary — the swollen base containing the ovules, each with an egg cell (female gamete).
All the pistils of a flower together form the gynoecium. After fertilisation the ovule becomes the seed and the ovary becomes the fruit.
❌ Why the other options are incorrect
✗ Stamen — the male reproductive part, made of anther + filament; the anther produces pollen grains. All stamens together form the androecium.
✗ Sepal — the green, outermost accessory whorl (calyx) that only protects the flower bud before it opens.
✗ Petal — the brightly coloured accessory whorl (corolla) that attracts insects and birds for pollination.
📌 SSC & Railway Exam Facts
• Pistil/Carpel = stigma + style + ovary; Stamen = anther + filament.
• Essential whorls — androecium and gynoecium; accessory whorls — calyx and corolla.
• A flower with both stamens and pistil is bisexual (hibiscus, mustard); with only one it is unisexual (papaya, watermelon).
• Pollination is the transfer of pollen from anther to stigma — self- or cross-pollination.
• Angiosperms show double fertilisation, first described by S. G. Nawaschin.

Correct Answer: Option 2 — 3
Isotopes are atoms of the same element having the same atomic number (Z) but different mass numbers (A) — they differ only in the number of neutrons. Hydrogen is the classic example and has three naturally occurring isotopes:
• Protium (₁H¹) — 1 proton, 0 neutrons; abundance about 99.98%; the only atom in nature with no neutron.
• Deuterium (₁H², D) — 1 proton, 1 neutron; it forms heavy water, D₂O, used as a moderator in nuclear reactors.
• Tritium (₁H³, T) — 1 proton, 2 neutrons; it is radioactive and occurs only in traces.
All three show the same chemical properties because each has the same electronic configuration (1 electron); only their physical properties (mass, density, boiling point) differ.
❌ Why the other options are incorrect
✗ 5 — hydrogen isotopes heavier than tritium (H-4 to H-7) have been made artificially and live for less than a fraction of a second; they do not exist in nature.
✗ 2 — this counts only protium and deuterium and leaves out tritium, which does occur naturally in trace amounts.
✗ 1 — 1 is the atomic number of hydrogen (its number of protons and electrons), not the number of its isotopes.
📌 SSC & Railway Exam Facts
• Isotopes — same Z, different A (₆C¹² and ₆C¹⁴; ₁₇Cl³⁵ and ₁₇Cl³⁷).
• Isobars — same mass number, different atomic number (₂₀Ca⁴⁰ and ₁₈Ar⁴⁰).
• Heavy water (D₂O) is a moderator in nuclear reactors; C-14 is used for carbon dating.
• U-235 is used in nuclear reactors, Co-60 in cancer therapy, I-131 for thyroid/goitre.
• Average atomic mass of chlorine is 35.5 u because Cl-35 and Cl-37 occur in a 3 : 1 ratio.

Correct Answer: Option 4 — Aluminium
How a metal behaves with water depends entirely on its position in the reactivity series:
• Very reactive metals (K, Na, Ca) react with cold water.
• Magnesium does not react with cold water but does react with hot water.
• Aluminium, zinc and iron react only with steam, not with cold or hot water.
• Copper, silver and gold do not react with water at all.
Aluminium therefore matches the question exactly. With steam it gives aluminium oxide and hydrogen gas.
⚗️ The Reaction
2Al(s) + 3H₂O(g) → Al₂O₃(s) + 3H₂(g)
• The water must be in the gaseous (steam) state, shown by the (g).
• A metal oxide — not a hydroxide — is formed, because the hydroxide cannot survive the temperature of steam.
• Compare: 2Na + 2H₂O → 2NaOH + H₂ (cold water) and Mg + 2H₂O → Mg(OH)₂ + H₂ (hot water).
❌ Why the other options are incorrect
✗ Potassium — the most reactive of the four; it reacts violently with cold water, and the hydrogen released catches fire at once.
✗ Sodium — also reacts vigorously with cold water to give NaOH and H₂; it is stored under kerosene for this reason.
✗ Magnesium — it does not react with cold water but does react with hot water to give Mg(OH)₂, so it is not a "steam only" metal.
📌 SSC & Railway Exam Facts
• Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > (H) > Cu > Hg > Ag > Au.
• Na and K are stored under kerosene to keep them away from air and moisture.
• Metals below hydrogen (Cu, Hg, Ag, Au) cannot displace hydrogen from dilute acids.
• Aluminium resists corrosion because a thin protective layer of Al₂O₃ forms on its surface.
• Gold and platinum are the least reactive metals and occur in the native (free) state.

Correct Answer: Option 3 — Atomic mass units (amu)
Atoms are extraordinarily light — one hydrogen atom weighs about 1.67 × 10⁻²⁴ g — so grams and kilograms are hopelessly clumsy for them. Chemists therefore use a relative unit, the atomic mass unit (amu, symbol u).
Since 1961 the standard has been the carbon-12 atom: 1 u = 1/12 of the mass of one ¹²C atom ≈ 1.66 × 10⁻²⁷ kg. Because the scale is relative, an atomic mass such as 16 u simply means that the atom is 16 times heavier than one-twelfth of a carbon-12 atom.
Examples: H = 1 u, C = 12 u, N = 14 u, O = 16 u, Na = 23 u, Cl = 35.5 u. The modern symbol is u (unified atomic mass unit), also called the dalton (Da).
❌ Why the other options are incorrect
✗ Grams per mole (g/mol) — this is the unit of molar mass, the mass of one mole (6.022 × 10²³ particles), not of a single atom. It is numerically equal to the atomic mass but is a different physical quantity.
✗ Kilograms — the SI unit of mass, far too large here; an atom's mass in kg comes to about 10⁻²⁶–10⁻²⁷, an unusable figure for everyday chemistry.
✗ Pounds — an imperial (FPS) unit used for commercial weighing; it has no role in atomic measurement.
📌 SSC & Railway Exam Facts
• 1 u = 1/12 the mass of a ¹²C atom = 1.66 × 10⁻²⁷ kg.
• Avogadro's number = 6.022 × 10²³; one mole of any substance contains this many particles.
• Molar mass in g/mol is numerically equal to the atomic or molecular mass in u.
• Earlier reference standards were hydrogen (Dalton) and then oxygen; carbon-12 was adopted in 1961.
• The atomic mass unit is also called the dalton (Da), named after John Dalton.

Correct Answer: Option 4 — Evaporation increases with increase in surface area.
Evaporation is a surface phenomenon: only those particles that lie at the surface of the liquid and happen to possess enough kinetic energy can break free of the attraction of their neighbours and escape as vapour.
If the surface area is increased, a larger number of particles are exposed at the surface at any moment, so more of them get a chance to escape every second. Hence the rate of evaporation is directly proportional to the surface area. This is exactly why wet clothes dry faster when spread out than when left in a heap, and why hot tea cools faster when poured into a saucer.
The four factors controlling evaporation are temperature, surface area and wind speed (all directly proportional) and humidity (inversely proportional).
❌ Why the other options are incorrect
✗ Evaporation increases with decrease in surface area — the exact reverse of the truth; a smaller surface exposes fewer particles and slows evaporation.
✗ Evaporation decreases with increase in surface area — again reversed; enlarging the exposed surface always speeds up evaporation.
✗ No effect of surface area on evaporation process — surface area is one of the four main factors; since evaporation happens only at the surface, it can never be independent of surface area.
📌 SSC & Railway Exam Facts
• Rate of evaporation ∝ temperature, ∝ surface area, ∝ wind speed, and ∝ 1/humidity.
• Evaporation is a cooling process — the escaping particles take the latent heat of vaporisation from the surroundings.
• Evaporation occurs at every temperature and only at the surface; boiling occurs at a fixed temperature throughout the liquid.
• Water stays cool in an earthen pot because it evaporates through the pot's pores.
• On a humid day clothes dry slowly, because the surrounding air already holds a lot of water vapour.

Correct Answer: Option 1 — Gold
Metals lying at the bottom of the reactivity series are so unreactive that they do not combine with the oxygen, moisture or other elements present in the earth's crust. They are therefore found uncombined, that is, in the free or native state. Gold, silver and platinum (and partly copper) are the metals found this way.
Gold (Au) is the classic example — it is the least reactive common metal, it does not tarnish in air, it is not attacked by water or by ordinary acids, and it dissolves only in aqua regia (a 3 : 1 mixture of conc. HCl and conc. HNO₃). Because of this inertness, nuggets of pure gold occur naturally in rocks and river beds.
Metals higher up the series are too reactive to survive uncombined and always occur as oxides, sulphides or carbonates, i.e. as ores, which must be reduced to obtain the metal.
❌ Why the other options are incorrect
✗ Zinc — a moderately reactive metal; it occurs as zinc blende (ZnS) and calamine (ZnCO₃), never in the free state.
✗ Aluminium — highly reactive; found as bauxite (Al₂O₃·2H₂O) and extracted only by electrolysis of molten alumina.
✗ Sodium — one of the most reactive metals of all; it reacts violently even with cold water, so it cannot exist free and is stored under kerosene.
📌 SSC & Railway Exam Facts
• Metals found in the native/free state: gold, silver, platinum and partly copper.
• Aqua regia = 3 parts conc. HCl + 1 part conc. HNO₃; it dissolves gold and platinum.
• The purity of gold is measured in carats; 24-carat gold is pure, ornaments are made of 22-carat.
• Highly reactive metals (K, Na, Ca, Mg, Al) are obtained by electrolytic reduction.
• Important ores: bauxite (Al), haematite (Fe₂O₃), zinc blende (ZnS), cinnabar (HgS), copper pyrites (CuFeS₂).

Correct Answer: Option 4 — Liquid state
Bromine (Br), atomic number 35, belongs to Group 17 — the halogens. It is the only non-metal that is a liquid at room temperature — a dense, reddish-brown, fuming liquid with a sharp, choking smell (its name comes from the Greek *bromos*, meaning "stench"). Its melting point is −7.2 °C and its boiling point is 58.8 °C.
Most non-metals are either gases (hydrogen, nitrogen, oxygen, fluorine, chlorine and the noble gases) or brittle solids (carbon, sulphur, phosphorus, iodine). Bromine is the single liquid exception among the non-metals, just as mercury (Hg) is the single liquid exception among the metals — a pairing asked again and again in exams.
❌ Why the other options are incorrect
✗ Plasma state — plasma is the fourth state of matter, a super-heated ionised gas found in the Sun, stars and fluorescent tubes; it is not the ordinary state of bromine.
✗ Solid state — the solid non-metals are iodine, sulphur, phosphorus and carbon; bromine is not solid at room temperature (it freezes only below −7.2 °C).
✗ Gaseous state — bromine fumes and vapourises easily, which is misleading, but at 25 °C it is definitely a liquid; fluorine and chlorine are the gaseous halogens.
📌 SSC & Railway Exam Facts
• Bromine is the only liquid non-metal; mercury is the only liquid metal at room temperature.
• Gallium (≈30 °C) and caesium (≈28 °C) are metals that melt with the heat of the palm.
• Halogens (Group 17): F₂ and Cl₂ are gases, Br₂ is a liquid, I₂ and At are solids.
• Iodine is the non-metal with a metallic lustre; graphite is the non-metal that conducts electricity.
• Diamond, an allotrope of carbon, is the hardest natural substance known.

Correct Answer: Option 1 — Niels Bohr
Niels Bohr (1913) proposed the planetary model of the atom, in which electrons revolve around the nucleus much as the planets revolve around the Sun, but only in certain fixed circular paths called orbits, shells or energy levels — K, L, M, N…
His main postulates were:
• Electrons revolve only in discrete (quantised) energy levels, and while in such an orbit they do not radiate energy — this makes the atom stable.
• Each shell has a definite energy; energy is absorbed when an electron jumps to a higher shell and emitted as light when it falls to a lower one.
• The maximum number of electrons a shell can hold is 2n² — K = 2, L = 8, M = 18, N = 32.
This removed the biggest flaw of Rutherford's model, which could not explain why a revolving electron does not lose energy and spiral into the nucleus.
❌ Why the other options are incorrect
✗ Ernest Rutherford — he gave the nuclear model after the α-scattering experiment; his electrons had no fixed energy levels, which left his atom unstable.
✗ J.J. Thomson (Joseph John Thomson) — he discovered the electron and gave the plum-pudding (watermelon) model, which had no nucleus and no orbits at all.
✗ Dmitri Mendeleev — a periodic table chemist, not an atomic-model physicist; he arranged the elements in order of increasing atomic mass.
📌 SSC & Railway Exam Facts
• Bohr won the Nobel Prize in Physics, 1922; the Bohr–Bury scheme governs the filling of shells.
• Maximum electrons in a shell = 2n²; the outermost shell can never hold more than 8 electrons.
• Atomic models in order: Dalton → Thomson → Rutherford → Bohr → quantum (Schrödinger).
• Valence electrons are the electrons of the outermost shell; they decide valency and chemical behaviour.
• Electron — J.J. Thomson (1897); proton — Goldstein; neutron — Chadwick (1932).

Correct Answer: Option 3 — Gold and platinum
The reactivity series arranges metals in decreasing order of their tendency to lose electrons:
K > Na > Ca > Mg > Al > Zn > Fe > Pb > (H) > Cu > Hg > Ag > Au
Metals at the bottom of this series are so unreactive that they do not combine with the oxygen, water or other elements present in the earth's crust. They are therefore found uncombined — in the native or free state. Gold (Au) and platinum (Pt) are the two most typical examples; silver and partly copper are also found free.
Gold does not tarnish, is unaffected by water and by dilute acids, and dissolves only in aqua regia (conc. HCl : conc. HNO₃ = 3 : 1). Platinum is equally inert, which is why it is used for laboratory electrodes and crucibles.
❌ Why the other options are incorrect
✗ Sodium and potassium — the most reactive metals of the series; they react violently even with cold water and are stored under kerosene, so they can never occur free.
✗ Calcium and aluminium — both are highly reactive; calcium occurs as limestone (CaCO₃) and gypsum (CaSO₄·2H₂O), aluminium as bauxite, and both are obtained by electrolytic reduction.
✗ Calcium and magnesium — both reactive metals found as carbonates and sulphates; magnesium even burns in air with a dazzling white flame.
📌 SSC & Railway Exam Facts
• Native/free-state metals: gold, silver and platinum (and partly copper).
• Aqua regia = conc. HCl : conc. HNO₃ = 3 : 1; it dissolves gold and platinum.
• Highly reactive metals (K, Na, Ca, Mg, Al) are extracted by electrolytic reduction.
• Moderately reactive metals (Zn, Fe, Pb, Cu) are extracted by roasting/calcination followed by reduction with carbon.
• In the standard series the most reactive metal is potassium and the least reactive is gold.

Correct Answer: Option 3 — E Rutherford
Ernest Rutherford discovered the nucleus in 1911 through his famous alpha-particle scattering (gold foil) experiment. He directed a beam of fast α-particles (He²⁺) at a very thin gold foil and recorded where they landed on a zinc sulphide screen.
His observations and conclusions were:
• Most α-particles passed straight through → the atom is mostly empty space.
• A few were deflected through small angles → there is a concentrated positive charge inside the atom.
• About 1 in 12,000 rebounded → all the positive charge and nearly all the mass are packed into a tiny central body, which he named the nucleus.
He also concluded that the electrons revolve around the nucleus, and that the nucleus is about 10⁻¹⁵ m across — roughly one hundred-thousandth of the size of the whole atom.
❌ Why the other options are incorrect
✗ J Chadwick — James Chadwick discovered the neutron (1932), the neutral particle inside the nucleus, not the nucleus itself.
✗ JJ Thomson — he discovered the electron (1897) using a cathode ray tube and gave the plum-pudding model, which had no nucleus at all.
✗ Neils Bohr — Niels Bohr improved Rutherford's model by introducing fixed energy levels (orbits); he did not discover the nucleus.
📌 SSC & Railway Exam Facts
• Rutherford — nucleus (1911); Thomson — electron (1897); Chadwick — neutron (1932); Goldstein — proton (canal rays).
• Rutherford is called the Father of Nuclear Physics; Nobel Prize in Chemistry, 1908.
• The α-particle Rutherford used is a helium nucleus, He²⁺.
• Nucleus ≈ 10⁻¹⁵ m; atom ≈ 10⁻¹⁰ m — the atom is about 10⁵ times larger than its nucleus.
• Protons and neutrons together are called nucleons; mass number = number of nucleons.

Correct Answer: Option 1 — atom
An atom is the smallest particle of an element that takes part in a chemical reaction and still retains all the chemical properties of that element. The word comes from the Greek *a-tomio*, meaning "indivisible", and the idea was first given scientific shape by John Dalton (1808) in his atomic theory.
An atom is built from three fundamental particles — protons (+) and neutrons (neutral) inside the nucleus, and electrons (−) revolving around it. If an atom is broken down into these particles, the identity and the properties of the element are lost: a lone proton is no longer "carbon" or "oxygen".
The corresponding smallest particle of a substance that can exist independently is the molecule.
❌ Why the other options are incorrect
✗ compound — a compound is formed from two or more different elements chemically combined in a fixed ratio; it is not a particle of a single element at all.
✗ electron — a sub-atomic particle carrying a negative charge. Electrons are identical in every element, so an electron by itself carries none of an element's characteristic properties.
✗ proton — also a sub-atomic particle, positively charged. Its number decides which element we have, but a free proton on its own does not show the properties of that element.
📌 SSC & Railway Exam Facts
• Atom = smallest particle of an element; molecule = smallest particle of a substance that can exist freely.
• Dalton's atomic theory (1808) first stated that matter is made of indivisible atoms.
• Atomic radius is measured in nanometres (1 nm = 10⁻⁹ m); atoms are about 10⁻¹⁰ m across.
• Atomic number (Z) = number of protons; mass number (A) = protons + neutrons.
• The word atom goes back to Democritus; the modern symbols of elements were given by Berzelius.

Correct Answer: Option 1 — Na₂CO₃·10H₂O
Washing soda is sodium carbonate decahydrate, Na₂CO₃·10H₂O — sodium carbonate crystallised together with 10 molecules of water of crystallisation. It is a white crystalline solid, basic in nature (pH about 11), and is obtained by recrystallising soda ash (anhydrous Na₂CO₃), which itself is manufactured by the Solvay (ammonia–soda) process.
The middle dot in the formula is important: the 10H₂O is water of crystallisation, chemically bound inside the crystal, not surface moisture. On heating, washing soda loses this water and becomes white powdery anhydrous Na₂CO₃.
Uses: softening hard water, washing clothes, in the glass, soap and paper industries, and as a common laboratory reagent.
❌ Why the other options are incorrect
✗ Al₂(SO₄)₃·10H₂O — a hydrate of aluminium sulphate; aluminium sulphate and potash alum are used for purifying water and to stop bleeding, not as washing soda.
✗ Na₂SO₄·10H₂O — this is Glauber's salt (sodium sulphate decahydrate), used as a laxative and in the glass industry; here the radical is sulphate, not carbonate.
✗ Al₂(CO₃)₃·10H₂O — aluminium carbonate is not even a stable compound; this option is fabricated only to mislead.
📌 SSC & Railway Exam Facts
• Washing soda = Na₂CO₃·10H₂O; soda ash = anhydrous Na₂CO₃; baking soda = NaHCO₃.
• Baking powder = baking soda + a mild edible acid (tartaric acid); it releases CO₂ and makes cakes rise.
• Bleaching powder = CaOCl₂, made by passing Cl₂ over dry slaked lime, Ca(OH)₂.
• Plaster of Paris = CaSO₄·½H₂O, obtained by heating gypsum (CaSO₄·2H₂O) to about 100 °C.
• Blue vitriol = CuSO₄·5H₂O, green vitriol = FeSO₄·7H₂O, Glauber's salt = Na₂SO₄·10H₂O.

Correct Answer: Option 1 — Barium sulphate
This is a classic double displacement (precipitation) reaction. Both reactants are soluble salts taken in aqueous solution, and of the two products, sodium chloride remains dissolved (aq) while barium sulphate is insoluble in water and separates out immediately as a thick white precipitate — that is, as a solid.
⚗️ The Reaction
Na₂SO₄(aq) + BaCl₂(aq) → 2NaCl(aq) + BaSO₄(s)
• The two compounds exchange their ions — Ba²⁺ pairs with SO₄²⁻, and Na⁺ pairs with Cl⁻.
• BaSO₄ is insoluble, so it is written with (s) and appears as a white precipitate.
• The coefficient 2 before NaCl is needed to balance the Na and Cl atoms.
Because an insoluble solid is formed, the reaction is also called a precipitation reaction.
❌ Why the other options are incorrect
✗ Sodium chloride — common salt is highly soluble in water, so it stays in solution as NaCl(aq); it is a product, but not the solid one.
✗ Barium chloride — this is a reactant, and it is taken as a soluble aqueous solution, so it is neither a product nor a solid here.
✗ Sodium sulphate — also a reactant and soluble in water; it is used as Na₂SO₄(aq).
📌 SSC & Railway Exam Facts
• BaSO₄ is an insoluble white precipitate; it is given as a barium meal for X-ray imaging of the stomach and intestines.
• Common white precipitates: BaSO₄, AgCl, PbSO₄, CaCO₃; yellow ones: PbI₂, AgBr.
• AgNO₃ + NaCl → AgCl↓ (white) + NaNO₃ is the standard precipitation PYQ.
• State symbols: (s) solid, (l) liquid, (g) gas, (aq) aqueous solution; a ↓ also marks a precipitate.
• All sodium and potassium salts are soluble in water; most sulphates are soluble except BaSO₄, PbSO₄ and CaSO₄.

Correct Answer: Option 4 — positive; negative
In the New Cartesian Sign Convention for spherical lenses, all distances are measured from the optical centre of the lens, distances measured in the direction of the incident light are taken positive and those measured against it are taken negative.
A convex lens is a converging lens — a beam of light parallel to the principal axis meets at a real focus on the far side of the lens, i.e. on the side where the light is travelling. Hence its focal length f is positive.
A concave lens is a diverging lens — the parallel beam spreads out and only appears to come from a virtual focus on the same side as the incoming light. Hence its focal length f is negative.
The same signs carry over to power, P = 1/f (in metres): a convex lens has positive power and a concave lens negative power.
❌ Why the other options are incorrect
✗ negative; positive — this reverses the two lenses; it would make the converging lens diverging and vice versa.
✗ positive; positive — a concave lens can never have a positive focal length because its focus is virtual.
✗ negative; negative — a convex lens forms a real focus, so its focal length cannot be negative.
📌 SSC & Railway Exam Facts
• Lens formula: 1/v − 1/u = 1/f; mirror formula: 1/v + 1/u = 1/f.
• Power of a lens, P = 1/f (m); SI unit dioptre (D), and 1 D = 1 m⁻¹.
• Convex lens → f positive, used to cure hypermetropia (long sight); concave lens → f negative, used to cure myopia (short sight).
• For mirrors, a concave mirror has negative f and a convex mirror positive f in the same convention.
• Magnification of a lens, m = v/u = h'/h.

Correct Answer: Option 2 — 5 m
📖 Given
• Initial velocity, u = 10 m/s (upwards)
• Final velocity at the highest point, v = 0 m/s
• Acceleration due to gravity, g = 10 m/s² (acting downwards, so a = −10 m/s²)
• To find: maximum height, h
✍️ Formula
v² = u² + 2as, which for vertical upward motion becomes v² = u² − 2gh
🔢 Solution
• 0² = (10)² − 2 × 10 × h
• 0 = 100 − 20h
• 20h = 100
• h = 100/20
• h = 5 m
In plain language: at the topmost point the object stops for an instant, and the whole of its kinetic energy has been converted into potential energy, which happens 5 m above the throwing point.
❌ Why the other options are incorrect
✗ 20 m — this comes from using h = u²/(2g) with g = 2.5, or from doubling the correct answer; it is not supported by the data.
✗ 100 m — this is simply u² = 100 written as a height, forgetting to divide by 2g.
✗ 1 m — this comes from dividing u by 2g (10/20 = 0.5) or similar mis-substitution; the velocity must be squared first.
📌 SSC & Railway Exam Facts
• Maximum height for vertical projection: h = u²/2g; time of ascent t = u/g.
• Here time of ascent = 10/10 = 1 s, and total time of flight = 2 s.
• The body returns to the thrower's hand with the same speed 10 m/s (ignoring air resistance).
• g = 9.8 m/s² on the Earth (often taken as 10), 1.63 m/s² on the Moon, and zero at the centre of the Earth.
• g is maximum at the poles and minimum at the equator, and it decreases with height as well as with depth.

Correct Answer: Option 3 — +1.5D
📖 Given
• Power of the converging (convex) lens, P₁ = +4.50 D (positive, because a convex lens converges light)
• Power of the diverging (concave) lens, P₂ = −3.00 D (negative, because a concave lens diverges light)
• The two lenses are placed in contact with each other
✍️ Formula
For thin lenses in contact, P = P₁ + P₂ (powers simply add algebraically)
🔢 Solution
• P = (+4.50) + (−3.00)
• P = 4.50 − 3.00
• P = +1.5 D
The positive sign tells us the combination as a whole still behaves like a converging lens, but a weaker one; its focal length is f = 1/P = 1/1.5 = 0.67 m ≈ 66.7 cm.
❌ Why the other options are incorrect
✗ −7.5D — obtained by adding the two magnitudes and then wrongly making the answer negative (4.5 + 3.0 = 7.5).
✗ −1.5D — the right magnitude but the wrong sign; it would mean the combination diverges, which is wrong because the converging lens is the stronger of the two.
✗ −13.5D — obtained by multiplying 4.5 by 3, which is not how powers combine.
📌 SSC & Railway Exam Facts
• Lenses in contact: P = P₁ + P₂ + P₃ … and 1/f = 1/f₁ + 1/f₂ + …
• Power P = 1/f (in metres); SI unit dioptre (D), so f = 1/P.
• Convex lens → power positive; concave lens → power negative.
• A lens of focal length 50 cm = 0.5 m has a power of +2 D.
• An optician's prescription of −2.5 D means a concave lens of focal length 40 cm, used for myopia.

Correct Answer: Option 4 — A satellite in a circular orbit around the earth.
Uniform circular motion is the motion of a body along a circular path with a constant speed. Its speed does not change, but because the direction of motion changes continuously, the velocity keeps changing — so uniform circular motion is an accelerated motion.
A satellite revolving in a circular orbit around the Earth covers equal arcs in equal times at a constant speed while the gravitational pull of the Earth acts as the centripetal force that keeps bending it into a circle. This is the textbook example of uniform circular motion.
The acceleration in such motion is the centripetal acceleration a = v²/r, always directed towards the centre, and the speed of one revolution is v = 2πr/T.
❌ Why the other options are incorrect
✗ A person walking on a sidewalk — this is motion along a straight line (rectilinear motion), not along a circle.
✗ A car driving straight on a highway — again a straight-line motion; there is no continuous change of direction.
✗ A bird flying in the sky — the bird's path is random and irregular, and its speed also varies, so it is neither circular nor uniform.
📌 SSC & Railway Exam Facts
• In uniform circular motion the speed is constant but the velocity is variable, so it is an accelerated motion.
• Centripetal force F = mv²/r acts towards the centre; the outward "centrifugal force" is a pseudo force.
• v = 2πr/T, where T is the time period of one revolution.
• Other examples: the Moon around the Earth, the tip of a clock's second hand, a stone whirled on a string.
• If the string breaks, the stone flies off along the tangent to the circle — an example of inertia of direction.

Correct Answer: Option 3 — Isaac Newton
Sir Isaac Newton, in 1666, was the first to pass a narrow beam of sunlight through a glass prism and obtain a band of seven colours on a screen. He named this band the spectrum. The splitting of white light into its constituent colours is called dispersion.
The seven colours in order are VIBGYOR — Violet, Indigo, Blue, Green, Yellow, Orange, Red. Dispersion happens because the refractive index of glass is different for different colours: violet has the shortest wavelength and bends the most, while red has the longest wavelength and bends the least.
Newton went further and showed that the spectrum could be recombined into white light by placing a second, inverted prism next to the first — proving that the colours were present in sunlight itself and not created by the prism.
❌ Why the other options are incorrect
✗ Einstein — Albert Einstein explained the photoelectric effect and gave the theory of relativity; he did not perform the prism experiment.
✗ Edison — Thomas Alva Edison invented the practical electric bulb and the phonograph; his work was in electricity, not optics.
✗ Fermi — Enrico Fermi built the first nuclear reactor and worked in nuclear physics.
📌 SSC & Railway Exam Facts
• Dispersion = splitting of white light into its seven colours; VIBGYOR is the order from the base of the prism upward.
• Violet deviates most, red deviates least; violet λ ≈ 400 nm, red λ ≈ 700 nm.
• A rainbow is a natural spectrum formed by refraction, total internal reflection and dispersion in water droplets.
• Newton's disc, when spun rapidly, appears white — showing that the seven colours combine into white light.
• Newton also gave the three laws of motion and the law of universal gravitation.

Correct Answer: Option 3 — time = distance/speed
When a body is not accelerating, its speed remains constant — this is uniform motion, in which the body covers equal distances in equal intervals of time.
For such motion the basic relation is
Speed = Distance / Time, i.e. v = s/t.
Rearranging this single relation gives the two other correct forms:
Distance = Speed × Time and Time = Distance / Speed.
Only Option 3, time = distance/speed, is one of these correct rearrangements, so it is the answer. A quick unit check confirms it: metre ÷ (metre/second) = second, which is indeed a time.
❌ Why the other options are incorrect
✗ distance = time/speed — units give second ÷ (m/s) = s²/m, which is not a length; the correct form is distance = speed × time.
✗ distance = speed/time — units give (m/s) ÷ s = m/s², which is an acceleration, not a distance.
✗ speed = time/distance — this is the reciprocal of speed; its unit would be s/m, not m/s.
📌 SSC & Railway Exam Facts
• v = s/t, s = v × t, t = s/v — the same relation written three ways.
• SI unit of speed is m/s; 1 m/s = 3.6 km/h and 1 km/h = 5/18 m/s.
• In uniform motion acceleration = 0 and the distance–time graph is a straight sloping line, its slope giving the speed.
• In non-uniform motion the distance–time graph is a curve.
• Average speed = total distance / total time; for uniform motion it equals the instantaneous speed.

Correct Answer: Option 1 — (u + v)/2
Average velocity is defined as the total displacement divided by the total time taken. When a body moves with uniform acceleration, its velocity changes at a steady rate, so the average velocity over a time interval is simply the arithmetic mean of the initial and the final velocity:
v(av) = (u + v)/2
This works because for uniform acceleration the velocity–time graph is a straight line; the area under it (the displacement) equals the area of a trapezium, which is the mean height × base, i.e. ((u + v)/2) × t.
So, for example, a car that speeds up uniformly from 20 m/s to 40 m/s has an average velocity of (20 + 40)/2 = 30 m/s over that interval.
❌ Why the other options are incorrect
✗ u + v — this is the sum of the two velocities; it is always larger than the final velocity itself, which is impossible for an average.
✗ (u − v)/2 — this uses the difference of the velocities; (v − u) is related to change in velocity, which gives acceleration when divided by time, not average velocity.
✗ 0 — the average velocity is zero only when the net displacement is zero, for example after one complete circular round; it is not a general result.
📌 SSC & Railway Exam Facts
• Average velocity = total displacement/total time; average speed = total distance/total time.
• v(av) = (u + v)/2 holds only for uniformly accelerated motion.
• The three equations of motion: v = u + at, s = ut + ½at², v² = u² + 2as.
• Displacement can also be written as s = ((u + v)/2) × t.
• Velocity is a vector, speed a scalar; both have SI unit m/s.

Correct Answer: Option 1 — 125 watt
📖 Given
• Work done by the machine, W = 500 J
• Time taken, t = 4 s
• To find: power output, P
✍️ Formula
Power = Work done / Time taken, i.e. P = W/t
🔢 Solution
• P = 500/4
• P = 125 W (125 watt)
In plain language: the machine delivers 125 joules of energy every second, and that rate of doing work is exactly what we call its power.
❌ Why the other options are incorrect
✗ 2000 watt — obtained by multiplying 500 × 4 instead of dividing; that gives the wrong quantity altogether.
✗ 250 watt — this is 500 ÷ 2, i.e. taking t = 2 s instead of 4 s.
✗ 8000 watt — this comes from multiplying 2000 by 4 again, compounding the earlier mistake.
📌 SSC & Railway Exam Facts
• P = W/t; SI unit watt (W), where 1 W = 1 J/s, named after James Watt.
• 1 horsepower (hp) = 746 W; 1 kilowatt = 1000 W.
• Commercial unit of electrical energy: 1 kWh = 1 unit = 3.6 × 10⁶ J.
• Work W = F × s × cos θ; SI unit joule (J), and 1 J = 1 N m.
• Electrical power can also be written as P = VI = I²R = V²/R.

Correct Answer: Option 3 — R(e) = 1 Ω, I = 10 A
📖 Given
• Battery voltage, V = 10 V
• R1 = 2 Ω, R2 = 3 Ω, R3 = 6 Ω
• The three resistors are joined in parallel
• To find: effective resistance R(e) and total current I
✍️ Formula
For a parallel combination, 1/R(e) = 1/R1 + 1/R2 + 1/R3, and by Ohm's law, I = V/R(e)
🔢 Solution
• 1/R(e) = 1/2 + 1/3 + 1/6
• Taking LCM 6: 1/R(e) = 3/6 + 2/6 + 1/6
• 1/R(e) = 6/6 = 1
• R(e) = 1 Ω
• I = V/R(e) = 10/1
• I = 10 A
Note that the effective resistance 1 Ω is smaller than the smallest individual resistance (2 Ω) — that is always true for a parallel combination, because the current gets extra paths to flow through.
❌ Why the other options are incorrect
✗ R(e) = 1 Ω, I = 1 A — the resistance is right but the current is wrong; 10 V across 1 Ω must give 10 A, not 1 A.
✗ R(e) = 2 Ω, I = 10 A — 2 Ω is just R1; the parallel formula was not applied, and 10 V across 2 Ω would give only 5 A.
✗ R(e) = 2 Ω, I = 1 A — both values are wrong; this ignores the parallel combination as well as Ohm's law.
📌 SSC & Railway Exam Facts
• Series: R(s) = R1 + R2 + R3 (resistance increases); Parallel: 1/R(p) = 1/R1 + 1/R2 + 1/R3 (resistance decreases).
• In parallel the voltage is the same across each resistor; in series the current is the same through each.
• Branch currents here: 10/2 = 5 A, 10/3 = 3.33 A, 10/6 = 1.67 A, total = 10 A — which checks the answer.
• Ohm's law: V = IR; SI unit of resistance ohm (Ω), of current ampere (A), of potential difference volt (V).
• Domestic appliances are connected in parallel so that each gets the full 220 V and can be switched independently.

Correct Answer: Option 1 — Only (iii)
The principal focus (F) of a spherical mirror is the point on the principal axis at which rays parallel to the principal axis converge after reflection (concave mirror) or from which they appear to diverge (convex mirror). The crucial words are "rays parallel to the principal axis".
Statement (i) is true — the principal focus always lies on the principal axis, midway between the pole P and the centre of curvature C, so f = R/2.
Statement (ii) is true — this is one of the standard ray-diagram rules: a ray that passes through the focus before striking the mirror comes back parallel to the principal axis (the reverse of the defining property).
Statement (iii) is NOT true — only rays parallel to the principal axis meet at the focus, not all incident rays. Rays coming from any other direction meet somewhere else, and parallel rays inclined to the axis meet on the focal plane, not at F. Hence only (iii) is untrue.
❌ Why the other options are incorrect
✗ Only (ii) and (iii) — statement (ii) is a correct ray-diagram rule, so it cannot be included.
✗ Only (i) — statement (i) is true; the focus is by definition a point on the principal axis.
✗ Only (i) and (ii) — both of these statements are true, so neither of them qualifies as "NOT true".
📌 SSC & Railway Exam Facts
• Focal length f = R/2, where R is the radius of curvature.
• A concave mirror has a real focus; a convex mirror has a virtual focus.
• Mirror formula: 1/v + 1/u = 1/f; magnification m = −v/u = h'/h.
• Concave mirrors are used as shaving mirrors, dentist's mirrors, headlight reflectors and solar concentrators.
• Convex mirrors are used as rear-view mirrors because they give an erect, diminished image and a wider field of view.

Correct Answer: Option 3 — 10 A
📖 Given
• Total charge, Q = 1200 C
• Time, t = 2 min
• 1 min = 60 s, so t = 2 × 60 = 120 s
• To find: electric current, I
✍️ Formula
Electric current = Charge / Time, i.e. I = Q/t
🔢 Solution
• t = 2 × 60 = 120 s
• I = 1200/120
• I = 10 A
In plain language: 10 coulomb of charge crosses any section of the circuit every second, and that rate of flow of charge is what an ammeter reads as 10 amperes.
❌ Why the other options are incorrect
✗ 60 A — this is the number of seconds in a minute, mistakenly written as the answer; it also results from dividing 1200 by 20.
✗ 100 A — obtained by wrongly using t = 12 s instead of 120 s, i.e. a decimal-place slip.
✗ 600 A — obtained by dividing 1200 by 2 and forgetting to convert minutes into seconds — the most common mistake in this question.
📌 SSC & Railway Exam Facts
• I = Q/t; SI unit of current is the ampere (A), and 1 A = 1 C/s.
• Charge on one electron = 1.6 × 10⁻¹⁹ C; so 1 C ≈ 6.25 × 10¹⁸ electrons.
• Current is a scalar quantity even though it has a direction of flow.
• Conventional current flows from the positive to the negative terminal, opposite to the direction of electron flow.
• An ammeter is connected in series (low resistance) and a voltmeter in parallel (high resistance).

Correct Answer: Option 2 — Right
This is an application of Newton's first law of motion (the law of inertia) — in particular of the inertia of direction, which is the tendency of a body to keep moving along the same straight line unless an unbalanced external force changes its direction.
While the car moves straight, the passenger is also moving straight ahead with the same velocity. When the car suddenly turns left, the seat and the floor turn left with the car, but the passenger's body tries to keep going in the original straight-line direction. Relative to the turning car, therefore, the person is thrown towards the right, i.e. outwards from the curve.
The outward push the passenger feels is often called the centrifugal force, but this is only a pseudo (fictitious) force; the real force in the situation is the centripetal force provided by friction between the tyres and the road, which is what actually turns the car.
❌ Why the other options are incorrect
✗ Forward — a forward lurch happens when the car brakes suddenly (inertia of motion), not when it turns.
✗ Backward — a backward push happens when a stationary car suddenly accelerates (inertia of rest).
✗ Left — the person leans away from the direction of the turn, not into it; leaning left would need a force pushing them inward.
📌 SSC & Railway Exam Facts
• Three kinds of inertia: inertia of rest, inertia of motion and inertia of direction.
• Centripetal force F = mv²/r acts towards the centre; centrifugal force is a pseudo force in the rotating frame.
• Roads at curves are banked (raised on the outer edge) so that a component of the normal reaction supplies the centripetal force.
• A cyclist leans inward while turning to generate the necessary centripetal force.
• Mass is the measure of inertia — heavier bodies resist changes of motion more strongly.

Correct Answer: Option 4 — virtual, erect and enlarged
For a concave mirror, when the object is placed between the pole (P) and the principal focus (F), the reflected rays diverge after reflection and never actually meet in front of the mirror. They only appear to come from a point behind the mirror, so the image formed is:
virtual, erect (upright) and enlarged (magnified), and it lies behind the mirror.
This is exactly why a concave mirror is used as a shaving mirror and as a dentist's mirror — the face or the tooth is kept closer to the mirror than its focus, giving a large, upright image.
This is the only position of an object in front of a concave mirror that gives a virtual image; for every other position (at F, between F and C, at C, beyond C) the image is real and inverted.
❌ Why the other options are incorrect
✗ real and diminished — a real, diminished image is formed when the object is placed beyond the centre of curvature C.
✗ virtual and diminished — a virtual and diminished image is the signature of a convex mirror, not a concave one.
✗ real and enlarged — a real, enlarged image is formed when the object lies between F and C, not between P and F.
📌 SSC & Railway Exam Facts
• Concave mirror image positions: object at infinity → at F, real, highly diminished; beyond C → between F and C, real, diminished; at C → at C, real, same size; between C and F → beyond C, real, enlarged; at F → at infinity; between P and F → behind mirror, virtual, erect, enlarged.
• Mirror formula: 1/v + 1/u = 1/f; magnification m = −v/u.
• m is positive for a virtual, erect image and negative for a real, inverted image; |m| > 1 means enlarged.
• A convex mirror always gives a virtual, erect and diminished image, whatever the object's position.
• f = R/2, so a mirror with R = 20 cm has a focal length of 10 cm.