RRB Technician Grade III 2024-25 28 December 2024 Shift 2 GK Questions – with answers & solutions

Correct Answer: Option 3 — Mustard
A bisexual flower (also called a perfect or hermaphrodite flower) carries both the male reproductive part, the stamen (anther + filament), and the female reproductive part, the pistil or carpel (stigma, style and ovary), in the same flower. The mustard flower is the standard NCERT example of such a flower — it has four sepals, four petals, six stamens and one pistil.
In contrast, a unisexual flower carries only stamens (staminate) or only the pistil (pistillate). After pollination, the pollen grain grows a pollen tube down the style to reach the ovule; the male gamete fuses with the female gamete in fertilisation, forming the zygote.
❌ Why the other options are incorrect
✗ Watermelon — bears unisexual flowers; male and female flowers are separate but occur on the same plant (monoecious).
✗ Pumpkin — the classic NCERT example of a unisexual flower; its large yellow male and female flowers are easy to tell apart.
✗ Papaya — a dioecious plant; male and female flowers are borne on different plants altogether.
📌 SSC & Railway Exam Facts
• Bisexual flowers: mustard, hibiscus (China rose), rose, pea, tomato, brinjal.
• Unisexual flowers: pumpkin, cucumber, watermelon, papaya, maize, coconut.
• A flower with all four whorls (calyx, corolla, androecium, gynoecium) is called a complete flower.
• Stamen = anther + filament; pistil = stigma + style + ovary.
• Self-pollination is common in bisexual flowers; cross-pollination is the rule in unisexual ones.

Correct Answer: Option 4 — Amphibians
Amphibians (frogs, toads, salamanders) and most reptiles have a three-chambered heart — two atria and a single undivided ventricle. Oxygenated blood returning from the lungs and skin enters the left atrium, while deoxygenated blood from the body enters the right atrium. Both empty into the one ventricle, so the two streams mix to some extent before being pumped out.
This mixing means the body tissues receive blood of mixed oxygen content. Such animals are cold-blooded (poikilothermic) — their body temperature changes with the surroundings — so their oxygen demand is lower and mixed blood is sufficient for them.
❌ Why the other options are incorrect
✗ Fishes — have a two-chambered heart (one atrium, one ventricle) with single circulation; blood passes through the heart only once per complete circuit.
✗ Mammals — have a four-chambered heart with complete separation of oxygenated and deoxygenated blood, needed for their high energy requirement.
✗ Birds — also have a four-chambered heart; being warm-blooded (homeothermic) they need highly efficient oxygen supply.
📌 SSC & Railway Exam Facts
• Heart chambers: Fish – 2, Amphibians & most Reptiles – 3, Crocodile, Birds & Mammals – 4.
• The crocodile is the only reptile with a four-chambered heart.
• Double circulation (blood passes twice through the heart in one cycle) occurs in birds and mammals.
• The frog also performs cutaneous respiration (breathing through moist skin) while in water.
• The human heart's valves prevent backflow — the tricuspid on the right and the bicuspid (mitral) on the left.

Correct Answer: Option 3 — ribosomes
The endoplasmic reticulum (ER) is a large network of membrane-bound tubes and sheets inside the cytoplasm. When tiny, dense granules called ribosomes sit on its outer surface, the membrane appears granular or rough under the microscope, and it is called Rough Endoplasmic Reticulum (RER).
Ribosomes are the sites of protein synthesis. The proteins they make on the RER are sent into the ER channels and then transported to various parts of the cell or exported out of it. Smooth Endoplasmic Reticulum (SER), which has no ribosomes, makes lipids and helps detoxify poisons and drugs in liver cells.
❌ Why the other options are incorrect
✗ protein particles — proteins are the product made by ribosomes; loose protein particles are not attached to the ER and do not make it look rough.
✗ lysosomes — membrane-bound sacs of digestive enzymes that clear worn-out organelles; called the suicide bags of the cell, they float free in the cytoplasm.
✗ chromosomes — thread-like DNA–protein structures that lie inside the nucleus and carry hereditary information; they never attach to the ER.
📌 SSC & Railway Exam Facts
• Ribosomes were discovered by George Palade; they are made of RNA and protein and have no membrane.
• Ribosome types: 70S in prokaryotes and in mitochondria/chloroplasts, 80S in eukaryotic cytoplasm.
• The ER gives internal framework (cytoplasmic skeleton) and acts as a transport channel within the cell.
• Golgi apparatus (discovered by Camillo Golgi) packages and dispatches what the ER makes.
• Mitochondrion = powerhouse of the cell; plastids are found only in plant cells.

Correct Answer: Option 2 — Only (i)
Non-biodegradable substances are materials that cannot be broken down by the action of micro-organisms such as bacteria and fungi — examples are plastic, polythene, DDT, glass, metal cans and aluminium foil.
Statement (i) is correct: because they cannot be decomposed, these substances build up in soil and water, choke drains, are swallowed by cattle and marine animals, and pass up the food chain by biomagnification, harming many members of the ecosystem.
Statement (ii) is wrong — the very definition of non-biodegradable is that biological processes do not break them down.
Statement (iii) is wrong — such substances persist in the environment for decades or even centuries.
❌ Why the other options are incorrect
✗ (i), (ii) and (iii) — wrong, because (ii) and (iii) contradict the definition of a non-biodegradable substance.
✗ Only (ii) and (iii) — wrong; these are exactly the two false statements, and it also leaves out the true statement (i).
✗ Only (i) and (ii) — (i) is true but (ii) is false, so the pair cannot be correct.
📌 SSC & Railway Exam Facts
• Biodegradable wastes: vegetable peels, paper, cotton, cow dung, wood, jute.
• DDT entering a food chain is the classic example of biomagnification; its concentration is highest in the top consumer.
• Only about 10% of energy passes from one trophic level to the next — the 10 per cent law of Lindemann.
• Because energy is lost at each step, food chains generally have only 3 to 4 trophic levels.
• Reduce, Reuse, Recycle is the three-R approach to waste management.

Correct Answer: Option 4 — Thyroid gland
The thyroid gland is a butterfly-shaped endocrine gland lying in the neck in front of the trachea. It secretes the hormone thyroxine (T4) and tri-iodothyronine (T3), and iodine is essential for making them — each molecule of thyroxine carries four iodine atoms.
Thyroxine regulates the metabolism of carbohydrates, proteins and fats in the body and thereby controls the rate at which energy is released. If iodine in the diet is insufficient, the gland cannot make enough thyroxine, enlarges, and the person develops goitre — a visibly swollen neck. This is why iodised salt is recommended.
❌ Why the other options are incorrect
✗ Pineal gland — a tiny gland in the brain that secretes melatonin and regulates the sleep–wake cycle; it does not need iodine.
✗ Pancreas — a mixed gland; its endocrine part secretes insulin and glucagon to control blood sugar, not thyroxine.
✗ Thymus — secretes thymosin and helps in the maturation of T-lymphocytes for immunity; it shrinks after puberty.
📌 SSC & Railway Exam Facts
• The thyroid is the largest endocrine gland in the human body.
• Iodine deficiency causes goitre; in children it causes cretinism (stunted growth, mental retardation).
• Excess thyroxine causes Grave's disease / hyperthyroidism; deficiency in adults causes myxoedema.
• The thyroid is stimulated by TSH from the anterior pituitary.
• The parathyroid glands, embedded behind the thyroid, secrete parathormone, which controls calcium balance.

Correct Answer: Option 1 — Small intestine
The small intestine is the longest part of the alimentary canal, measuring about 6 to 7 metres in an adult human. It is highly coiled so that this great length fits into the abdominal cavity. Its three parts are the duodenum, jejunum and ileum.
The small intestine is the site of complete digestion of carbohydrates, proteins and fats — it receives bile from the liver, pancreatic juice from the pancreas and intestinal juice from its own walls. Its inner lining bears millions of finger-like projections called villi, which hugely increase the surface area for absorption of digested food into the blood.
❌ Why the other options are incorrect
✗ Large intestine — only about 1.5 metres long; it absorbs water and salts from the undigested food and forms faeces.
✗ Food pipe (oesophagus) — about 25 cm long; it merely carries the swallowed food from the mouth to the stomach by peristalsis.
✗ Stomach — a J-shaped muscular bag, not the longest part; it churns food and digests protein with pepsin in an acidic medium made by HCl.
📌 SSC & Railway Exam Facts
• The small intestine is longest in herbivores (they digest cellulose) and shorter in carnivores.
• The liver is the largest gland in the body; bile emulsifies fats into small globules.
• Appendix is a vestigial organ attached to the large intestine.
• Salivary amylase (ptyalin) starts starch digestion in the mouth.
• The complete alimentary canal in humans is about 9 metres long.

Correct Answer: Option 2 — Testes secrete testosterone hormone.
The testes are the primary sex organs of the male. They perform two functions: they produce the male gamete, the sperm, inside the seminiferous tubules, and they secrete the male sex hormone testosterone from the interstitial (Leydig) cells lying between those tubules.
Testosterone brings about the secondary sexual characters of a boy at puberty — deepening of the voice, growth of facial and body hair, broadening of the shoulders — and it also regulates sperm production itself. Its release is controlled by LH from the pituitary gland.
❌ Why the other options are incorrect
✗ Sperm formation requires higher temperature than the normal body temperature — wrong; sperm formation needs a temperature about 2–3 °C lower than body temperature, which is why the testes hang outside in the scrotum.
✗ Formation of sperm takes place in seminal vessel — wrong; sperms are formed in the seminiferous tubules of the testes. The seminal vesicle only adds fluid to make semen.
✗ Testes are located in the abdominal cavity — wrong; in humans the testes lie outside the abdominal cavity in a skin pouch called the scrotum.
📌 SSC & Railway Exam Facts
• Male accessory glands: seminal vesicles, prostate gland and Cowper's (bulbourethral) gland.
• Sperms travel: testis → epididymis → vas deferens → urethra.
• In the male, the urethra is a common passage for both urine and semen.
• A human sperm carries 23 chromosomes — either an X or a Y; the Y sperm decides a male child.
• Testosterone is secreted by Leydig cells; Sertoli cells nourish the developing sperms.

Correct Answer: Option 4 — only in simple body organised multicellular organisms
Fragmentation is a mode of asexual reproduction in which the body of a multicellular organism breaks into two or more fragments, and each fragment grows into a new complete individual. The classic NCERT example is the filamentous green alga Spirogyra, which simply breaks up into smaller pieces on maturing.
Fragmentation is possible only in simple-bodied multicellular organisms, where the cells are not organised into specialised tissues and organs. In organisms with a complex body design, different organs perform different jobs, so a random broken piece cannot rebuild all the missing systems and cannot survive as a whole organism.
❌ Why the other options are incorrect
✗ in all multicellular organisms — wrong; complex multicellular animals such as humans, birds and mammals cannot reproduce by fragmentation.
✗ only in unicellular organisms — wrong; a unicellular organism has a single cell and reproduces by binary or multiple fission, not by fragmentation.
✗ only in complex body organised multicellular organisms — wrong; complexity of body design is exactly what prevents fragmentation.
📌 SSC & Railway Exam Facts
• Spirogyra — fragmentation; Planaria — regeneration; Hydra & yeast — budding.
• Regeneration is carried out by specialised cells and is different from fragmentation.
• Binary fission — Amoeba, Leishmania, Paramecium; multiple fission — Plasmodium.
• Spore formation occurs in Rhizopus (bread mould) inside sporangia.
• Offspring of asexual reproduction are genetically identical clones of the parent.

Correct Answer: Option 3 — Transpiration
Transpiration is the loss of water from the aerial parts of a plant — mainly the leaves — in the form of water vapour. It takes place chiefly through tiny pores called stomata, whose opening and closing is controlled by two bean-shaped guard cells.
Transpiration is not mere waste. It creates a transpiration pull, a suction force that draws a continuous column of water upward through the xylem from the roots to the topmost leaves — this is the main force for ascent of sap in tall trees. It also helps in the absorption and upward movement of minerals and in cooling the plant on hot days.
❌ Why the other options are incorrect
✗ Transportation — the general movement of water, food and minerals within the plant through xylem and phloem; it is not the loss of water as vapour.
✗ Transcription — a molecular process in which mRNA is synthesised from DNA; it has nothing to do with water loss.
✗ Imbibition — the absorption of water by solid colloids such as dry seeds or wood, causing them to swell; it is the opposite of losing water.
📌 SSC & Railway Exam Facts
• Loss of water as liquid droplets from leaf margins is guttation, not transpiration.
• Transpiration pull was explained by the cohesion–tension theory of Dixon and Joly.
• Translocation is the transport of prepared food through phloem, and it requires energy (ATP).
• Stomata mostly open in the day and close at night; in desert plants (CAM), the reverse happens.
• Transpiration is often called a necessary evil of plants.

Correct Answer: Option 4 — Flower
Vegetative propagation is a form of asexual reproduction in plants in which a new plant grows from a vegetative part — the root, stem or leaf — of the parent. Since no gametes fuse, the new plants are genetically identical clones of the parent.
The flower is the reproductive organ of a plant, not a vegetative part. It is the site of sexual reproduction: the anther makes pollen (male gamete) and the ovary holds the ovule (female gamete), and their fusion in fertilisation produces a seed with a genetically new combination. Hence the flower has no role in vegetative propagation.
❌ Why the other options are incorrect
✗ Leaves — do take part; Bryophyllum develops buds on its leaf margins that fall and grow into new plants.
✗ Stem — does take part; sugarcane, rose, grapes and potato (with its eye buds) are propagated by stem cuttings and tubers.
✗ Root — does take part; sweet potato, dahlia and Asparagus grow new shoots from their modified roots.
📌 SSC & Railway Exam Facts
• Natural methods: cutting, layering, grafting are the artificial ones used by gardeners.
• Tissue culture (micropropagation) raises thousands of plants from a few cells on a nutrient medium.
• Vegetative propagation lets seedless plants such as banana, orange and jasmine be grown.
• Plants so raised flower and fruit earlier than plants grown from seed.
• Its drawback is no variation, so a single disease can wipe out the whole crop.

Correct Answer: Option 1 — First, carbohydrates are utilised for energy production and the rest are stored in the form of starch.
In photosynthesis, green plants use sunlight, chlorophyll, carbon dioxide and water to make glucose and release oxygen. The reaction is: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (in the presence of sunlight and chlorophyll).
As NCERT states, the carbohydrate produced is used to provide energy to the plant, and the carbohydrates which are not used immediately are stored in the form of starch. Starch acts as the plant's internal energy reserve, drawn upon whenever needed. This is exactly why the iodine test, which turns starch blue-black, is used to show that photosynthesis has taken place in a leaf.
❌ Why the other options are incorrect
✗ All the carbohydrates are immediately used as energy — wrong; a plant makes far more glucose than it needs at that moment, and the surplus is stored.
✗ Carbohydrates are stored in the form of glycogen — wrong; glycogen is the storage carbohydrate of animals and fungi, stored in the liver and muscles, not of plants.
✗ All the carbohydrates are stored in the form of a starch — wrong; part of the glucose is used up at once for the plant's own respiration and growth.
📌 SSC & Railway Exam Facts
• Photosynthesis occurs in the chloroplast; chlorophyll is the green pigment that traps sunlight.
• Its two phases: the light reaction (in grana) and the dark reaction / Calvin cycle (in stroma).
• The oxygen released in photosynthesis comes from water, not from CO₂.
• Storage carbohydrate: starch in plants, glycogen in animals, cellulose builds the plant cell wall.
• Chlorophyll contains magnesium (Mg); haemoglobin contains iron (Fe).

Correct Answer: Option 1 — Plasmodium divides into many daughter cells simultaneously by binary fission.
This statement is incorrect because dividing into many daughter cells at the same time is multiple fission, not binary fission. In binary fission a parent cell splits into exactly two daughter cells. Plasmodium, the malarial parasite, undergoes multiple fission — its nucleus divides repeatedly inside the cell and then the cytoplasm splits around each nucleus, producing many daughter individuals at once.
Multiple fission also helps such parasites survive unfavourable conditions, as the parent encloses itself in a cyst and releases numerous daughter cells when conditions improve.
❌ Why the other options are incorrect (i.e. these statements are CORRECT)
✗ Binary fission occurs in a definite orientation in Leishmania — correct; Leishmania has a whip-like flagellum at one end, and fission always takes place in a definite plane with respect to it.
✗ Yeast can put out small buds that separate and grow further — correct; yeast reproduces by budding, the bud growing on the parent and later detaching.
✗ In Amoeba, the splitting of the two cells during division can take place in any plane — correct; Amoeba has no fixed body shape, so binary fission can occur in any plane.
📌 SSC & Railway Exam Facts
• Binary fission — Amoeba, Leishmania, Paramecium, bacteria; multiple fission — Plasmodium.
• Malaria is caused by Plasmodium and spread by the female Anopheles mosquito.
• Leishmania causes kala-azar, spread by the sandfly.
• Budding — yeast and Hydra; fragmentation — Spirogyra; regeneration — Planaria and Hydra.
• Amoeba moves and feeds using pseudopodia (false feet).

Correct Answer: Option 3 — Kala-azar
Kala-azar, also called visceral leishmaniasis or black fever, is caused by the protozoan parasite Leishmania donovani. It is transmitted by the bite of the female sandfly (Phlebotomus).
The parasite attacks the spleen, liver and bone marrow, causing prolonged fever, enlargement of the spleen and liver, weight loss, anaemia and darkening of the skin — from which the name *kala* (black) *azar* (fever) comes. In biology it is equally famous as an example of binary fission in a definite orientation, because Leishmania has a flagellum at one end that fixes the plane of division.
❌ Why the other options are incorrect
✗ Anaemia — not an infection by Leishmania; it is a deficiency disease caused chiefly by lack of iron, resulting in low haemoglobin.
✗ Dengue — caused by the dengue virus, spread by the Aedes aegypti mosquito; known as break-bone fever and marked by a fall in platelets.
✗ Malaria — caused by the protozoan Plasmodium, spread by the female Anopheles mosquito; it reproduces by multiple fission.
📌 SSC & Railway Exam Facts
• Protozoan diseases: malaria (Plasmodium), kala-azar (Leishmania), amoebic dysentery (Entamoeba), sleeping sickness (Trypanosoma).
• Bacterial: typhoid, cholera, tuberculosis, tetanus, anthrax, plague.
• Viral: AIDS, influenza, dengue, polio, rabies, common cold, COVID-19.
• Vector-borne diseases spread through mosquitoes, flies and sandflies.
• Ronald Ross received the Nobel Prize for discovering the malaria transmission cycle in mosquitoes.

Correct Answer: Option 3 — length
Meristematic tissue consists of actively dividing cells with thin cell walls, dense cytoplasm, prominent nuclei and no vacuoles. Apical meristem is present at the growing tips of the stem and the root, and its continuous division increases the length of the plant — this is called primary growth.
Plant growth is thus limited to certain regions only, unlike in animals. The three types of meristem are apical (increases length), lateral or cambium (increases girth) and intercalary (at the base of leaves or internodes, seen in grasses).
❌ Why the other options are incorrect
✗ girth — the increase in thickness or girth is caused by the lateral meristem (cambium), giving secondary growth, not by apical meristem.
✗ flowers — flowers arise when a vegetative bud turns into a floral bud under hormonal control; apical meristem itself does not produce flowers.
✗ branches — branches develop from axillary (lateral) buds present in the leaf axil, not from the apical meristem at the tip.
📌 SSC & Railway Exam Facts
• Intercalary meristem is found at the base of leaves or internodes — that is why grass regrows after mowing.
• Meristematic cells are undifferentiated; they later mature into permanent tissues.
• Simple permanent tissues: parenchyma, collenchyma, sclerenchyma; complex: xylem and phloem.
• Removing the apex (decapitation) promotes branching by ending apical dominance, which is caused by auxin.
• Annual rings formed by the cambium are used to estimate the age of a tree.

Correct Answer: Option 3 — 27 u
The mass number (A) of an atom is the total number of protons and neutrons present in its nucleus. Protons and neutrons together are called nucleons, and each of them has a mass of very nearly 1 u. The electron weighs only about 1/1836 u, so its contribution to the mass of the atom is neglected.
Here the atom has 13 protons and 14 neutrons, so A = 13 + 14 = 27. Since the atomic number (Z) = number of protons = 13, the element is aluminium, written in standard notation as ²⁷₁₃Al.
Remember that Z decides which element the atom is, while A decides which isotope of that element it is.
⚗️ The Calculation
A = Z + n = 13 + 14 = 27
• Z = 13 (protons) → the element is aluminium (Al).
• Number of neutrons n = A − Z = 27 − 13 = 14.
• A neutral Al atom also has 13 electrons, giving the electronic configuration 2, 8, 3.
❌ Why the other options are incorrect
✗ 14 u — this is only the number of neutrons; the 13 protons have been forgotten.
✗ 1 u — this is the mass of a single proton or neutron, not of the whole atom.
✗ 13 u — this is the atomic number (number of protons), which is written as a subscript, not the mass number.
📌 SSC & Railway Exam Facts
• Mass number (A) = protons + neutrons; atomic number (Z) = protons.
• Standard notation places A above and Z below: ²⁷₁₃Al, ³⁵₁₇Cl.
• Isotopes — same Z, different A (¹H, ²H, ³H); isobars — same A, different Z (⁴⁰Ca and ⁴⁰Ar).
• Mass of a proton ≈ mass of a neutron ≈ 1 u = 1.66 × 10⁻²⁷ kg.
• The neutron was discovered by James Chadwick (1932); it carries no charge.

Correct Answer: Option 2 — They turn blue litmus paper red.
An acid is a substance that gives hydrogen ions, H⁺ (or H₃O⁺), in aqueous solution. It is these H⁺ ions that produce every typical acidic property — a sour taste, a pH below 7, the ability to conduct electricity, and the reddening of blue litmus.
Litmus is a natural indicator obtained from lichens. The rule to memorise is simple: acid turns blue litmus red, and base turns red litmus blue. A base also feels soapy or slippery and tastes bitter.
Acids also react with active metals to release hydrogen gas, and with carbonates to release carbon dioxide — both classic laboratory tests.
⚗️ The Reaction
Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)
• An acid supplies H⁺ ions, which are reduced by the metal to give hydrogen gas.
• The gas burns with a pop sound — the standard test for H₂.
• With a carbonate: Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂, and the CO₂ turns lime water milky.
❌ Why the other options are incorrect
✗ They have a pH greater than 7 — a pH above 7 means basic; acids always have pH < 7 (pH = 7 is neutral).
✗ They turn red litmus paper blue — this is the test for a base, not an acid.
✗ They have a slippery feel — the soapy, slippery touch belongs to bases such as NaOH and soap solution.
📌 SSC & Railway Exam Facts
• Acid → blue litmus red; base → red litmus blue.
• pH < 7 acidic, pH = 7 neutral, pH > 7 basic; the pH scale was given by S. P. L. Sørensen.
• Phenolphthalein: colourless in acid, pink in base; methyl orange: red in acid, yellow in base.
• Acid in the stomach is hydrochloric acid (HCl); lemon — citric acid, vinegar — acetic acid, curd — lactic acid.
• Onion and vanilla are olfactory indicators — they change smell, not colour.

Correct Answer: Option 3 — Calcium carbonate
A decomposition reaction is one in which a single compound breaks down into two or more simpler substances. When the energy needed is supplied as heat, it is called thermal decomposition.
Calcium carbonate (CaCO₃) — found as limestone, marble and chalk — decomposes on strong heating at about 1000 °C to give calcium oxide (CaO) and carbon dioxide (CO₂). In industry this is carried out in a lime kiln, and the process is called calcination. The CaO produced is known as quick lime, and on adding water it gives slaked lime, Ca(OH)₂, with a great deal of heat.
Decomposition reactions are endothermic, because energy must be supplied to break the compound apart.
⚗️ The Reaction
CaCO₃(s) → (heat) CaO(s) + CO₂(g)
• One reactant gives two products — the signature of a decomposition reaction.
• CaO = quick lime; CaO + H₂O → Ca(OH)₂ (slaked lime) is a highly exothermic combination reaction.
• The CO₂ released turns lime water milky, forming a white precipitate of CaCO₃.
❌ Why the other options are incorrect
✗ Calcium nitrate — Ca(NO₃)₂ decomposes on heating to give CaO, nitrogen dioxide (NO₂) and oxygen, not carbon dioxide; it contains no carbon at all.
✗ Calcium chloride — CaCl₂ is a thermally stable salt; it melts rather than decomposing into CaO and CO₂.
✗ Calcium sulphate — CaSO₄ needs a very high temperature and then gives CaO and sulphur trioxide (SO₃); again there is no carbon in it.
📌 SSC & Railway Exam Facts
• CaCO₃ → (heat) CaO + CO₂ — the classic thermal decomposition / calcination reaction.
• Limestone, marble, chalk all have the same formula, CaCO₃.
• Quick lime = CaO, slaked lime = Ca(OH)₂, lime water = dilute Ca(OH)₂ solution.
• Other PYQ decompositions: 2FeSO₄ → (heat) Fe₂O₃ + SO₂ + SO₃, 2Pb(NO₃)₂ → (heat) 2PbO + 4NO₂ + O₂.
• Decomposition by heat = thermal, by light = photolytic (2AgCl → (sunlight) 2Ag + Cl₂), by electricity = electrolytic.

Correct Answer: Option 3 — Na
The method used to extract a metal depends on its position in the reactivity series.
Metals of high reactivity — K, Na, Ca, Mg and Al — hold their ores so strongly that no chemical reducing agent (carbon, CO, aluminium) can reduce them. They are therefore obtained by the electrolytic reduction of their molten (fused) salts or oxides. Sodium is extracted by the electrolysis of molten sodium chloride in the Down's process: Na⁺ ions move to the cathode and are reduced to sodium metal, while Cl⁻ ions are oxidised to chlorine gas at the anode.
Metals of middle reactivity (Zn, Fe, Pb, Cu) are first converted to their oxides by roasting/calcination and then reduced with carbon. Metals of low reactivity (Ag, Au, Pt) occur free or need only mild heating.
⚗️ The Reaction
2NaCl(l) → (electrolysis) 2Na(s) + Cl₂(g)
• At the cathode (reduction): Na⁺ + e⁻ → Na.
• At the anode (oxidation): 2Cl⁻ → Cl₂ + 2e⁻.
• Aluminium is obtained the same way from molten Al₂O₃ in cryolite — the Hall–Héroult process.
❌ Why the other options are incorrect
✗ Zn — a moderately reactive metal; zinc oxide is reduced by carbon: ZnO + C → Zn + CO.
✗ Pb — also moderately reactive; PbO + C → Pb + CO, so carbon reduction is enough.
✗ Ag — a least reactive metal found largely in the free state; its ores are reduced very easily and it is refined, not extracted, electrolytically.
📌 SSC & Railway Exam Facts
• Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.
• Top of the series → electrolytic reduction; middle → carbon reduction; bottom → found free.
• Down's process → Na; Hall–Héroult process → Al.
• Roasting = heating a sulphide ore in excess air; calcination = heating a carbonate ore in limited air.
• In electrolytic refining, the impure metal is the anode, the pure metal the cathode, and the impurities settle as anode mud.

Correct Answer: Option 3 — catenation
Catenation is the ability of an element to form bonds with atoms of its own kind, producing long chains, branches and rings. Carbon shows catenation to the maximum extent of all elements, and this single property is the reason why more than 10 million organic compounds are known — far more than the compounds of all the other elements put together.
Carbon can do this because its C—C bond is exceptionally strong and stable (small atomic size, high bond energy) and because carbon is tetravalent — each carbon atom has 4 valence electrons and forms four covalent bonds, so it can hold other carbons and still have bonds left for hydrogen or other atoms.
Carbon chains may be straight (n-butane), branched (isobutane) or closed rings (cyclohexane, benzene), and the bonds may be single, double or triple.
❌ Why the other options are incorrect
✗ Isomerisation — the existence of compounds with the same molecular formula but different structures (e.g. C₄H₁₀ as n-butane and isobutane); it is a *consequence* of catenation, not the bonding property itself.
✗ cyclisation — the formation of a closed ring from an open chain; it is only one special case of catenation.
✗ Crystallisation — a purification technique used to obtain pure solid crystals from a solution; it has nothing to do with carbon–carbon bonding.
📌 SSC & Railway Exam Facts
• Catenation is strongest in carbon; next comes silicon, but its chains are short and unstable.
• Carbon is tetravalent (valency 4), atomic number 6, configuration 2, 4.
• Carbon forms covalent bonds by sharing electrons, so its compounds are poor conductors with low melting and boiling points.
• Allotropes of carbon: diamond (hardest natural substance), graphite (conducts electricity), fullerene (C₆₀, buckminsterfullerene).
• Compounds with the same molecular formula but different structures are isomers; the first alkane to show isomerism is butane (C₄H₁₀).

Correct Answer: Option 3 — Creating casts for supporting fractured bones
Plaster of Paris is calcium sulphate hemihydrate, CaSO₄·½H₂O. It is made by heating gypsum (CaSO₄·2H₂O) to about 373 K (100 °C), which drives off three-quarters of the water of crystallisation. Heating above this temperature must be avoided, because the anhydrous CaSO₄ (dead burnt plaster) formed then will no longer set.
When plaster of Paris is mixed with water it takes the water back and changes into gypsum again, setting within minutes into a hard, solid mass that expands slightly and does not shrink. This is why doctors use it in orthopaedic plaster casts to hold a fractured bone in position. It is also used for making statues, decorative mouldings, toys and blackboard chalk, and for fireproofing materials.
⚗️ The Reaction
CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O
• Setting is simply the rehydration of the hemihydrate back to gypsum.
• Preparation: CaSO₄·2H₂O → (373 K) CaSO₄·½H₂O + 1½H₂O.
• It must be stored in a moisture-proof container, or it sets in the bag.
❌ Why the other options are incorrect
✗ Fire extinguisher — this uses sodium hydrogen carbonate (baking soda, NaHCO₃), which releases CO₂ to smother the flame.
✗ Remove the hardness of water — washing soda (Na₂CO₃·10H₂O) removes hardness by precipitating Ca²⁺ and Mg²⁺ ions.
✗ Baking — the baking agent is baking soda (NaHCO₃) or baking powder, which liberates CO₂ and makes the cake rise.
📌 SSC & Railway Exam Facts
• Plaster of Paris = CaSO₄·½H₂O; gypsum = CaSO₄·2H₂O.
• It is prepared by heating gypsum to 373 K (100 °C); overheating gives dead burnt plaster.
• Baking soda = NaHCO₃, washing soda = Na₂CO₃·10H₂O, bleaching powder = CaOCl₂.
• Plaster of Paris gets its name from the large gypsum deposits at Montmartre, Paris.
• Antacids contain Mg(OH)₂ (milk of magnesia) or NaHCO₃ to neutralise excess stomach acid.

Correct Answer: Option 2 — They are very large in size.
The particle nature of matter rests on four established characteristics: matter is made of extremely small particles, these particles have space between them, they are continuously moving (they possess kinetic energy), and they attract one another with an intermolecular force of attraction.
Particles of matter are in fact unimaginably small — so small that a few crystals of potassium permanganate can colour a very large volume of water, and the smell of an incense stick spreads across a whole room. Therefore the statement that they are very large in size is NOT a characteristic of matter, and it is the required answer.
The continuous motion of particles causes diffusion, which becomes faster on heating because the kinetic energy of the particles increases.
❌ Why the other options are incorrect
✗ They have space between them — this is true; the intermolecular space is largest in gases and smallest in solids, which is why gases are highly compressible.
✗ They attract each other — this is true; the force of attraction is strongest in solids, moderate in liquids and weakest in gases.
✗ They are continuously moving — this is true; particles possess kinetic energy, which is why diffusion and Brownian motion occur.
📌 SSC & Railway Exam Facts
• Characteristics of particles of matter: very small size, space between them, continuous motion, mutual attraction.
• Intermolecular force: solid > liquid > gas; intermolecular space: gas > liquid > solid.
• Diffusion is fastest in gases and increases with temperature.
• The kinetic energy of particles is directly proportional to the absolute temperature.
• Zig-zag motion of suspended particles is Brownian motion, proof of the continuous motion of particles.

Correct Answer: Option 1 — 7
The pH scale measures the concentration of hydrogen ions (H⁺) in a solution. The letter p stands for the German *potenz* (power), so pH means the 'power of hydrogen'. The scale runs from 0 to 14 at 25 °C.
A solution is neutral when the concentration of H⁺ ions is exactly equal to the concentration of OH⁻ ions. In pure water at 25 °C both are 10⁻⁷ mol/L, which gives pH = 7. Hence a neutral solution such as pure water, common salt solution (NaCl) or glucose solution has a pH of 7.
pH below 7 → acidic (the smaller the number, the stronger the acid) and pH above 7 → basic (the larger the number, the stronger the base). Each unit change in pH means a ten-fold change in H⁺ concentration.
❌ Why the other options are incorrect
✗ 5 — a pH of 5 is acidic; black coffee (≈5) and acid rain (< 5.6) fall in this region.
✗ 14 — this is the upper end of the scale, the pH of a strongly basic solution such as concentrated sodium hydroxide.
✗ 0 — this is the lower end of the scale, the pH of a very strong acid such as concentrated hydrochloric acid.
📌 SSC & Railway Exam Facts
• pH < 7 acidic, pH = 7 neutral, pH > 7 basic; scale range 0–14.
• The pH scale was introduced by the Danish chemist S. P. L. Sørensen (1909).
• Human blood pH = 7.35–7.45 (slightly basic); saliva ≈ 6.5–7.5; gastric juice ≈ 1.2–3.0.
• Tooth decay begins when the pH in the mouth falls below 5.5; enamel is calcium phosphate, the hardest substance in the body.
• Rain is called acid rain when its pH is below 5.6; plants grow best in soil of pH ≈ 6.5–7.5.

Correct Answer: Option 3 — Copper (II) chloride
Copper oxide (CuO) is a black, basic metal oxide. A basic oxide reacts with an acid to give a salt and water — a neutralisation that is also a double displacement reaction.
In CuO, oxygen has an oxidation number of −2, so copper must be +2. When the acid replaces the oxide ion, copper keeps this +2 state, and each Cu²⁺ ion combines with two Cl⁻ ions to give CuCl₂ — copper(II) chloride. The Roman numeral (II) in the name is simply the oxidation state of copper.
The experiment is a favourite in textbooks because of the colour change: the black copper oxide dissolves and the solution turns a blue-green colour, which is the colour of copper(II) chloride in water.
⚗️ The Reaction
CuO(s) + 2HCl(aq) → CuCl₂(aq) + H₂O(l)
• Metal oxide + acid → salt + water — a neutralisation reaction.
• Cu²⁺ needs two Cl⁻ ions to balance its charge, giving the formula CuCl₂.
• The black solid disappears and a blue-green solution is formed.
❌ Why the other options are incorrect
✗ Copper (IV) chloride — would need Cu⁴⁺ and the formula CuCl₄; copper does not show a stable +4 state.
✗ Copper (I) chloride — CuCl is formed from copper(I) oxide, Cu₂O (red), not from the black CuO given here.
✗ Copper (III) chloride — CuCl₃ is not an ordinary compound; the common oxidation states of copper are only +1 and +2.
📌 SSC & Railway Exam Facts
• Acid + metal oxide → salt + water; metal oxides are basic, non-metal oxides are acidic.
• Roman numerals in a name give the oxidation state: FeCl₂ iron(II) chloride, FeCl₃ iron(III) chloride.
• CuO is black, Cu₂O is red; CuSO₄·5H₂O (blue vitriol) is blue and turns white on heating.
• Acid + metal → salt + H₂; acid + carbonate → salt + water + CO₂.
• Copper: symbol Cu (from *cuprum*), atomic number 29; a very good conductor used in wiring.

Correct Answer: Option 1 — C₃H₆ and C₄H₈
A homologous series is a family of organic compounds with the same general formula and the same functional group, in which each member differs from the next by a —CH₂— unit (14 u). Members of one series show similar chemical properties and a gradual change in physical properties.
Alkenes are unsaturated hydrocarbons containing at least one carbon–carbon double bond (C=C). Their general formula is CₙH₂ₙ, and the series begins with ethene (C₂H₄) because at least two carbon atoms are needed to form a double bond.
Testing the options against CₙH₂ₙ: C₃H₆ (n = 3, 2n = 6 ✓) is propene and C₄H₈ (n = 4, 2n = 8 ✓) is butene. Both are alkenes and they differ by exactly one CH₂, so this pair alone belongs to the alkene homologous series.
❌ Why the other options are incorrect
✗ CH₄ and C₂H₄ — CH₄ (methane) fits CₙH₂ₙ₊₂ and is an alkane; only C₂H₄ (ethene) is an alkene, so the pair is mixed.
✗ C₂H₆ and C₃H₁₀ — C₂H₆ (ethane) is an alkane, and C₃H₁₀ does not exist at all (propane is C₃H₈).
✗ CH₄ and C₄H₈ — again a mixture: CH₄ is an alkane while C₄H₈ (butene) is an alkene.
📌 SSC & Railway Exam Facts
• General formulas: alkane CₙH₂ₙ₊₂, alkene CₙH₂ₙ, alkyne CₙH₂ₙ₋₂.
• Successive members of a homologous series differ by CH₂, i.e. 14 u of molecular mass.
• First members: methane CH₄, ethene C₂H₄, ethyne C₂H₂ (acetylene).
• Saturated hydrocarbons (alkanes) burn with a clean blue flame; unsaturated ones burn with a yellow sooty flame.
• Unsaturation is tested with bromine water, whose brown colour is decolourised by alkenes and alkynes.

Correct Answer: Option 4 — oxides, sulphides and carbonates
The minerals from which a metal can be extracted profitably and conveniently are called its ores. Except for the least reactive metals (gold, silver, platinum), which occur in the free or native state, all metals are found in the crust in the combined state — chemically joined to oxygen, sulphur, carbonate, halide or sulphate groups.
So the ores of the Earth's crust are of many kinds together, the three commonest classes being:
• Oxides — bauxite (Al₂O₃·2H₂O), haematite (Fe₂O₃), zincite (ZnO)
• Sulphides — zinc blende (ZnS), cinnabar (HgS), copper glance (Cu₂S), galena (PbS)
• Carbonates — calamine (ZnCO₃), siderite (FeCO₃), limestone (CaCO₃), malachite
Because oxides are the easiest to reduce, sulphide ores are first roasted and carbonate ores calcined — both converting the ore into its oxide before reduction.
❌ Why the other options are incorrect
✗ only carbonates — carbonates are just one class of ore; haematite (oxide) and galena (sulphide) are equally important and disprove the word "only".
✗ only oxides — oxides are the commonest class, but zinc blende (ZnS) and calamine (ZnCO₃) show that other classes exist.
✗ only sulphides — sulphides are typical of the middle of the reactivity series; the ores of aluminium and iron are oxides, not sulphides.
📌 SSC & Railway Exam Facts
• Roasting — sulphide ore heated in excess air: 2ZnS + 3O₂ → 2ZnO + 2SO₂.
• Calcination — carbonate ore heated in limited air: ZnCO₃ → ZnO + CO₂.
• Aluminium — bauxite; Iron — haematite/magnetite; Zinc — zinc blende/calamine; Mercury — cinnabar; Lead — galena.
• Aluminium is the most abundant metal and oxygen the most abundant element in the Earth's crust.
• Gravity separation, froth flotation, magnetic separation and leaching are methods of concentrating an ore.

Correct Answer: Option 4 — The solute particles can be separated from the mixture by the process of filtration.
A true solution is a homogeneous mixture of two or more substances, made of a solute dissolved in a solvent. Its particles are smaller than 1 nm (10⁻⁹ m), which is far smaller than the pores of a filter paper.
Because of this extremely small size, the solute particles pass straight through filter paper and therefore cannot be separated by filtration. They also never settle down on standing, and they do not scatter light, so a true solution does not show the Tyndall effect and looks perfectly transparent.
A solute is recovered from a solution by evaporation, crystallisation or distillation, not by filtration. Hence statement 4 is false and is the required answer.
❌ Why the other options are incorrect
✗ The particles of a solution are smaller than 1 nm — true; this is the defining size limit of a true solution (colloid 1–1000 nm, suspension > 1000 nm).
✗ A solution is a homogenous mixture — true; the composition is uniform throughout and the solute cannot be seen as a separate phase.
✗ Because of very small particle size, particles do not scatter a beam of light — true; this is exactly why a true solution shows no Tyndall effect.
📌 SSC & Railway Exam Facts
• Solution = solute + solvent; water is the universal solvent.
• Particle size: true solution < 1 nm, colloid 1–1000 nm, suspension > 1000 nm.
• Tyndall effect is shown by colloids and suspensions, never by a true solution.
• Filtration separates a suspension; centrifugation separates a colloid; evaporation/crystallisation recovers a dissolved solute.
• Alloys (brass, bronze, steel) are solid solutions; air is a gaseous solution.

Correct Answer: Option 4 — Gold and silver
Whether a metal occurs free (native) or combined in the Earth's crust is decided entirely by its chemical reactivity.
Metals at the bottom of the reactivity series — copper, mercury, silver, gold and platinum — are very unreactive. They do not react readily with the oxygen, moisture, carbon dioxide or acids of the environment, so they survive in the crust as the metal itself. Gold and silver are the standard textbook examples of metals found in the free or native state; gold is so unreactive that ancient ornaments are still bright today.
Metals at the top of the series — potassium, sodium, calcium, magnesium and aluminium — are so reactive that they combine at once with air and water. Sodium and potassium even catch fire in air and react violently with cold water, which is why sodium is stored under kerosene and is never found free in nature.
❌ Why the other options are incorrect
✗ Sodium and potassium — both are extremely reactive; they react violently with cold water and are always found as compounds such as NaCl and KCl.
✗ Silver and potassium — silver is indeed found free, but potassium is one of the most reactive metals and never occurs in the native state.
✗ Gold and sodium — gold is found free, but sodium is highly reactive and occurs only in the combined state.
📌 SSC & Railway Exam Facts
• Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.
• Metals found native: gold (Au), silver (Ag), platinum (Pt), and sometimes copper.
• Sodium and potassium are stored under kerosene because they react vigorously with air and water.
• Gold is the most ductile and most malleable metal; its purity is measured in carats — 24 carat = pure gold.
• Silver is the best conductor of heat and electricity among all metals.

Correct Answer: Option 1 — force × displacement
Work is said to be done when a force acting on a body displaces it along the direction of that force. So work is the product of the force and the displacement produced in the direction of the force:
W = F × s
The SI unit of work is the joule (J), where 1 J = 1 N × 1 m. Work is a scalar quantity — it has magnitude but no direction. If the force makes an angle θ with the displacement, the general form is W = F s cos θ.
This is why a man pushing a heavy wall that does not move does zero work in physics — the displacement s is zero, however tired he may get.
❌ Why the other options are incorrect
✗ force / displacement — force divided by displacement gives a quantity measured in N/m, which is the spring constant (stiffness), not work.
✗ force − displacement — force is measured in newton and displacement in metre; quantities with different units can never be subtracted.
✗ force + displacement — same objection: only like physical quantities can be added together.
📌 SSC & Railway Exam Facts
• W = F s cos θ — work is positive at θ = 0°, zero at θ = 90° and negative at θ = 180°.
• SI unit of work and energy is the joule (J); the CGS unit is the erg; 1 J = 10⁷ erg.
• 1 joule of work is done when a force of 1 N moves a body through 1 m in its own direction.
• Work done against friction or by a body being lifted down by gravity is negative work.
• Power = Work / Time; SI unit watt (W), and 1 W = 1 J/s.

Correct Answer: Option 2 — Potential energy
Mechanical energy is the energy a body possesses because of its motion or because of its position/configuration. It therefore has exactly two parts:
• Kinetic energy (KE = ½mv²) — energy due to motion.
• Potential energy (PE = mgh) — energy due to position or state of strain.
Total mechanical energy = KE + PE. For a freely falling body (no friction), this total stays constant — that is the law of conservation of mechanical energy. As a stone falls, PE keeps converting into KE, but the sum never changes.
❌ Why the other options are incorrect
✗ Only Light energy — light (radiant) energy travels as electromagnetic waves; it is a separate form, not a part of mechanical energy.
✗ Only Heat energy — heat is the internal energy of random molecular motion; it is thermal energy, and mechanical energy lost to friction turns into it.
✗ Only Chemical energy — this is energy stored in the bonds of a fuel or food and is released in chemical reactions, not a form of mechanical energy.
📌 SSC & Railway Exam Facts
• Mechanical energy = Kinetic energy + Potential energy.
• KE = ½mv² and gravitational PE = mgh; both are measured in joule (J).
• A body at the highest point of its flight has maximum PE and minimum KE.
• Energy can neither be created nor destroyed — the law of conservation of energy.
• A stretched spring or bow stores elastic potential energy.

Correct Answer: Option 2 — Virtual and erect
When an object is placed between the pole (P) and the principal focus (F) of a concave mirror, the reflected rays diverge after reflection. They never actually meet, so they must be produced backwards; they appear to meet behind the mirror.
The image so formed is therefore virtual, erect and enlarged (magnified), and it lies behind the mirror. This is the only position of the object for which a concave mirror gives an erect image.
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 than the focus so that a big, upright image is seen.
❌ Why the other options are incorrect
✗ Real and inverted — a concave mirror gives a real, inverted image only when the object is at or beyond F, not between P and F.
✗ Virtual and inverted — impossible: a virtual image formed by a mirror is always erect.
✗ Real and erect — impossible for a single mirror: a real image formed by a mirror is always inverted.
📌 SSC & Railway Exam Facts
• Concave mirror, object between P and F → virtual, erect, enlarged image behind the mirror.
• Object at C → image at C, real, inverted, same size; object at F → image at infinity.
• A convex mirror always forms a virtual, erect, diminished image, whatever the object position.
• Mirror formula 1/v + 1/u = 1/f; magnification m = −v/u = h'/h.
• For a spherical mirror, R = 2f (radius of curvature is twice the focal length).

Correct Answer: Option 3 — inertia
Inertia is the natural tendency of every body to resist any change in its state of rest or of uniform motion in a straight line. A body at rest wants to stay at rest and a body in motion wants to keep moving with the same speed in the same direction, until an unbalanced external force acts on it.
This idea is the content of Newton's First Law of Motion, which is therefore also called the Law of Inertia. The mass of a body is the direct measure of its inertia — a heavier body is harder to start and harder to stop.
Everyday examples: passengers jerk backwards when a bus starts suddenly (inertia of rest) and fall forward when it brakes suddenly (inertia of motion).
❌ Why the other options are incorrect
✗ motion — motion is simply the change of position of a body with time; it does not describe resistance to change.
✗ momentum — momentum is p = mv, the 'quantity of motion' a moving body carries; its SI unit is kg m/s.
✗ force — force is the external push or pull that overcomes inertia and changes the state of motion; its SI unit is the newton (N).
📌 SSC & Railway Exam Facts
• Newton's First Law = Law of Inertia; it was first stated in essence by Galileo.
• Mass is the measure of inertia — more mass means more inertia.
• Three types: inertia of rest, inertia of motion and inertia of direction.
• Newton's Second Law: F = ma; Third Law: action and reaction are equal and opposite.
• 1 newton is the force that gives a 1 kg mass an acceleration of 1 m/s².

Correct Answer: Option 2 — Distance
In free fall, the only force acting on the body is its weight, so the body moves with the constant acceleration due to gravity, g = 9.8 m/s² (taken as 10 m/s² in easy sums).
Because the body is accelerating, its speed keeps increasing every second, and the distance it has covered keeps growing — in fact s = ½gt², so the distance is not even growing uniformly. Therefore distance is the quantity that does not stay constant.
In the first second a freely falling body covers about 4.9 m, in the next second about 14.7 m — clear proof that distance changes continuously.
❌ Why the other options are incorrect
✗ Universal Gravitational Constant — G = 6.67 × 10⁻¹¹ N m² kg⁻² is a fixed constant of nature; it is the same everywhere in the universe.
✗ Acceleration — during free fall near the Earth's surface the acceleration stays fixed at g = 9.8 m/s², independent of the body's mass.
✗ Mass — the mass of a body is the amount of matter in it and never changes with position or motion; only its weight (W = mg) can change from place to place.
📌 SSC & Railway Exam Facts
• Equations of free fall: v = gt, s = ½gt², v² = 2gs (starting from rest).
• g = 9.8 m/s² on the Earth's surface; g = 1.625 m/s² on the Moon, about 1/6 of the Earth's.
• g is maximum at the poles and minimum at the equator; it is zero at the centre of the Earth.
• G is a universal constant; g is not — it varies with height, depth and latitude.
• In free fall all bodies fall together — a feather and a coin land together in a vacuum tube.

Correct Answer: Option 4 — current through the coil is increased
The magnetic field produced at the centre of a current-carrying circular coil is given by
B = μ₀nI / 2r
where I is the current, n the number of turns, r the radius of the coil and μ₀ the permeability of free space.
From this relation, B is directly proportional to the current I and directly proportional to the number of turns n. So doubling the current doubles the field. Increasing the current is therefore the correct way to make the field stronger — this is exactly how the strength of an electromagnet is controlled.
❌ Why the other options are incorrect
✗ One moves way from the coil — the field of a coil weakens rapidly as the distance from it increases.
✗ current through the coil is decreased — since B ∝ I, reducing the current reduces the magnetic field.
✗ number of turns of the coil is decreased — since B ∝ n, fewer turns give a weaker field.
📌 SSC & Railway Exam Facts
• Field at the centre of a circular coil: B = μ₀nI / 2r; inside a long solenoid: B = μ₀nI.
• SI unit of magnetic field (flux density) is the tesla (T); CGS unit is the gauss; 1 T = 10⁴ gauss.
• Direction of the field is found by the Right-Hand Thumb Rule (Maxwell's corkscrew rule).
• Oersted discovered in 1820 that a current-carrying wire deflects a magnetic needle.
• An electromagnet is strengthened by more turns, more current and a soft iron core.

Correct Answer: Option 1 — emerge parallel to the principal axis
This is one of the standard rules of ray diagrams for spherical mirrors. A ray that passes through the principal focus (F) of a concave mirror strikes the mirror and, after reflection, travels parallel to the principal axis.
The reason is the principle of reversibility of light — light retraces its own path. A ray coming parallel to the principal axis is reflected through F; therefore a ray going through F must be reflected parallel to the axis.
This property is used in torches, headlights and searchlights, where the bulb is placed at the focus of a concave reflector so that a strong parallel beam comes out.
❌ Why the other options are incorrect
✗ emerge obliquely to the principal axis — the reflected ray is exactly parallel, not slanting; the rule is definite, not approximate.
✗ pass through the principal focus — this happens to a ray that arrives parallel to the principal axis, which is the reverse case.
✗ pass through the centre of curvature — a ray retraces its path through C only when it strikes the mirror normally, i.e. it was already directed at C.
📌 SSC & Railway Exam Facts
• Ray parallel to axis → reflected through F; ray through F → reflected parallel to axis.
• Ray through C → retraces its own path (angle of incidence = 0°).
• Laws of reflection: ∠i = ∠r, and the incident ray, reflected ray and normal lie in the same plane.
• A concave mirror is a converging mirror; a convex mirror is a diverging mirror.
• f = R/2 for a spherical mirror; a concave mirror's f is taken negative in the sign convention.

Correct Answer: Option 1 — m s⁻²
📖 Given
• The physical quantity is acceleration (a).
• Acceleration is defined as the rate of change of velocity.
✍️ Formula
a = change in velocity / time = (v − u) / t
🔢 Solution
• Unit of velocity = m/s = m s⁻¹
• Unit of time = s
• Unit of acceleration = (m s⁻¹) / s = m s⁻²
So acceleration is measured in metre per second squared (m s⁻²) — it tells how much the velocity changes in every one second. Acceleration is a vector quantity; if it is negative it is called retardation or deceleration.
❌ Why the other options are incorrect
✗ m s² — this comes from multiplying by time instead of dividing by it; it is not the unit of any common quantity.
✗ m s⁻¹ — this is the SI unit of velocity or speed, one step before acceleration.
✗ m s — metre × second; it is not the unit of acceleration at all.
📌 SSC & Railway Exam Facts
• Acceleration due to gravity, g = 9.8 m s⁻², also written as 9.8 m/s².
• Equations of motion: v = u + at, s = ut + ½at², v² = u² + 2as.
• SI unit of force = newton (N) and 1 N = 1 kg m s⁻².
• In uniform circular motion the speed is constant but the body is still accelerated, because the direction keeps changing.
• The slope of a velocity–time graph gives the acceleration; its area gives the displacement.

Correct Answer: Option 1 — Incident
Refraction is the bending of light when it passes from one transparent medium into another, caused by the change in the speed of light in the two media.
The First Law of Refraction states that the incident ray, the refracted ray and the normal drawn to the interface at the point of incidence all lie in the same plane.
The Second Law of Refraction, known as Snell's Law, states that for a given pair of media the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant:
sin i / sin r = n₂₁ (the refractive index of medium 2 with respect to medium 1).
❌ Why the other options are incorrect
✗ Emergent — the emergent ray is the ray that finally leaves a glass slab or prism; it is not named in the first law of refraction.
✗ Parallel — 'parallel ray' is not a term of the laws of refraction; in a glass slab the emergent ray only happens to be parallel to the incident ray.
✗ Reflected — the reflected ray belongs to the laws of reflection, where ∠i = ∠r at a mirror surface.
📌 SSC & Railway Exam Facts
• Snell's Law: n₁ sin i = n₂ sin r, or sin i / sin r = constant.
• Refractive index n = c/v, where c = 3 × 10⁸ m/s is the speed of light in vacuum.
• Denser to rarer → ray bends away from the normal; rarer to denser → bends towards the normal.
• Refraction explains a stick looking bent in water, the twinkling of stars and the apparent flattening of the setting Sun.
• Refractive index of water = 1.33, glass ≈ 1.5, diamond = 2.42 (the highest of common materials).

Correct Answer: Option 1 — Both (i) and (iii)
A solenoid is a long coil of many circular turns of insulated copper wire wound closely like a cylinder.
Statement (i) is TRUE — inside a long current-carrying solenoid the field lines are straight, parallel and equally spaced, so the magnetic field there is uniform, given by B = μ₀nI.
Statement (iii) is TRUE — the pattern of field lines outside a solenoid is exactly like that of a bar magnet. One end behaves as the north pole and the other as the south pole, which is why a current-carrying solenoid is called an electromagnet.
Statement (ii) is FALSE — the field outside a long solenoid is very weak (nearly zero), not equal to the strong uniform field inside.
❌ Why the other options are incorrect
✗ Both (ii) and (iii) — it wrongly includes (ii); the outside field is almost zero, not equal to the inside field.
✗ Only(i) — it leaves out the true statement (iii) about the bar-magnet-like pattern.
✗ Only (iii) — it leaves out the true statement (i) about the uniform field inside.
📌 SSC & Railway Exam Facts
• Field inside a long solenoid: B = μ₀nI, where n is the number of turns per unit length.
• A solenoid with a soft iron core becomes a powerful electromagnet.
• Magnetic field lines are closed curves; they never intersect each other.
• Outside a magnet, field lines run north to south; inside, they run south to north.
• Electromagnets are used in electric bells, cranes, loudspeakers and MRI machines.

Correct Answer: Option 3 — opposite to the direction of motion
The force of gravity always acts vertically downwards, towards the centre of the Earth. When an object is thrown upward, its motion is directed upwards, so gravity is acting exactly opposite to the direction of motion.
Because the force opposes the motion, it produces a retardation of g = 9.8 m/s². The upward speed keeps falling until it becomes zero at the highest point. After that the object starts coming down, and now gravity is along the direction of motion, so it accelerates the body.
Note that during the upward journey the work done by gravity is negative, since force and displacement point in opposite directions.
❌ Why the other options are incorrect
✗ Zero — gravity never becomes zero near the Earth's surface; even at the highest point where v = 0, the acceleration is still g.
✗ the same as the direction of motion — this is true only while the body is falling down, not while it is going up.
✗ independent of direction of motion — gravity's own direction is fixed (downward), so relative to an upward motion it is definitely opposite, not unrelated.
📌 SSC & Railway Exam Facts
• Going up: v = u − gt; maximum height H = u²/2g; time of ascent t = u/g.
• Time of ascent = time of descent for a body thrown vertically up (air resistance neglected).
• The body returns to the thrower's hand with the same speed with which it was thrown.
• Weight W = mg; weight is a force measured in newton (N), mass is measured in kg.
• In free fall a body feels weightlessness, as in an orbiting spacecraft.

Correct Answer: Option 4 — 0m, 10m
📖 Given
• Maximum height reached upward, h = 5 m
• The body then falls back to the point from which it was thrown.
✍️ Formula
Distance = total length of the path actually travelled (a scalar)
Displacement = shortest straight line from the initial to the final position (a vector)
🔢 Solution
• Path travelled going up = 5 m
• Path travelled coming down = 5 m
• Total distance = 5 + 5 = 10 m
• The body ends exactly where it started, so initial and final positions are the same.
• Total displacement = 0 m
The body has certainly moved 10 m of path, but since it returned to the starting point, its net change of position is zero.
❌ Why the other options are incorrect
✗ 5m, 5m — this is the answer only for the upward journey alone; the return trip has been ignored.
✗ 0m, 0m — the displacement is right, but the distance can never be zero when a body has actually moved along a path.
✗ 10m, 0m — the two values have been interchanged; 10 m is the distance and 0 m is the displacement.
📌 SSC & Railway Exam Facts
• Distance is a scalar and is always positive; displacement is a vector and can be positive, negative or zero.
• Distance ≥ Displacement always; they are equal only for motion in a straight line without turning back.
• For one complete round of a circle of radius r: distance = 2πr, displacement = 0.
• SI unit of both distance and displacement is the metre (m).
• Average speed = total distance / total time; average velocity = total displacement / total time.